METHOD FOR DETERMINING TERM OF PREGNANCY

Abstract: This invention provides a method of early detection of other than term delivery in a pregnant human subject, the method comprising: measuring during the first or second trimester of that pregnancy the maternal level of corticotrophin-releasing hormone (CRH) or of another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species, found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that the delivery will occur other than at full term if the level of CRH or the other molecular species deviates from the normal level.

Description: "Method for Determining Term of Pregnancy" TECHNICAL FIELD The present invention relates to a method of determining an anticipated time for parturition in a pregnant human subject and in particular relates to a method for the early detection of premature or post- mature delivery by the subject. BACKGROUND ART Parturition is a transitional phase occupying the final three weeks of gestation in humans, characterised by a series of structural and functional changes in the myometriu , cervix and foetal membranes which culminate in the onset of labour and delivery of the baby. It has long been assumed that parturition is initiated by a hormonal event in late pregnancy, but no such event has yet been identified in human pregnancy 11) . Not all women undergo full term pregnancy and any given pregnancy may result in premature or post-mature delivery. A premature delivery may result in the birth of an underweight and immature baby that will require intensive medical management before the baby may return home with the mother. In severe cases, premature delivery may lead to brain damage and other severe complications or result in the death of the baby. Alternatively, a pregnancy may result in a post-mature delivery which may also have severe consequences to the mother and baby. It is therefore desirable to have a method of early detection or prediction that a given pregnancy may result in premature or post-mature delivery. DESCRIPTION OF THE INVENTION During the study of levels of corticotrophin- releasing hormone (CRH) and CRH-binding protein (CRH-BP) in pregnant humans, the present inventor has developed a method of determining an anticipated time for parturition in humans. The present inventor has shown that the timing of human parturition is influenced from an early stage in pregnancy by a longitudinal maturation process in the foetal-placental unit. Measurement of maternal CRH levels has been shown by the inventor to provide a marker for this process. Accordingly, in a first aspect the present invention consists in a method of early detection of premature delivery in a pregnant human subject, the method comprising: measuring during the first or second trimester of that pregnancy the maternal level of corticotrophin- releasing hormone (CRH) or of another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species, found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that the delivery will occur sooner than full term if the level of CRH is elevated relative to the normal level of CRH or if the level of the other molecular species deviates from the normal level in a manner indicative of advanced development of the foetal- placental unit. In a second aspect, the present invention consists in a method of early detection of post-mature delivery in a pregnant human subject comprising: measuring during the first or second trimester of that pregnancy the maternal level of corticotrophin- releasing hormone (CRH) or of another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that the delivery will occur later than full term if the level of CRH is depressed relative to the normal level of CRH or if the level of the other molecular species deviates from the normal level in a manner indicative of retarded development of the foetal- placental unit. In a third aspect, the invention provides a method for determining whether a pregnant human patient experiencing preterm uterine contractions is at risk of delivering prematurely the method comprising: measuring the maternal level of corticotrophin- releasing hormone (CRH) or another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that delivery is likely to occur prematurely if the level of CRH is elevated relative to the normal level of CRH or if the level of the other molecular species deviates from the normal level in a manner indicative of advanced development of the foetal- placental unit. Current practice when pregnant women present in apparent preterm labour is to commence treatment with salbutamol to try to stop the contractions. Recently, a group of researchers (22) have demonstrated that transder al nitric oxide donating agents may also provide effective treatment, permitting the pregnancy to progress to full term. The present inventor has shown in a randomised comparison of these two methods of treatment that some patients responded poorly to the administered therapy and delivered prematurely inspite of the therapy. In cases where this happened, the patient showed significantly elevated CRH levels, which indicates that labour was imminent. A significant problem for premature babies is lung immaturity. Foetal lungs can be matured by the administration of β methasone. However, if delivery is likely the β methasone needs to be administered quickly in order to permit lung maturation to occur prior to delivery. A method of determining that delivery is imminent and that consequently tocolytic therapy may not succeed can improve patient care by facilitating clinical decision making with regard to administration of agents such as steroids to mature foetal lungs. This treatment can be undertaken as a priority followed by a decision regarding persevering with tocolytic therapy. The levels of CRH can be measured in blood taken from the patient. Typically the levels are measured in the patient's plasma or serum. The levels of the other molecular species may increase, decrease or vary in some other fashion as pregnancy progresses. In order to be of use in prediction of delivery time, the level of the species present must correlate with stage of gestation. It will be understood that the levels of CRH or of the other molecular species can be measured directly or indirectly by a variety of techniques available to the skilled addressee. In a preferred embodiment of the first, second and third aspects, the measuring of CRH levels is by an immunological method. Preferably the immunological method is a radioimmunoassay. If a premature or post-mature delivery in a pregnancy of a human subject is detected by the methods of the present invention, then it is possible to instigate medical management of the pregnancy so as to result in an improved outcome for the foetus. Such medical management could include the transdermal application of nitric oxide donating drugs, administration of salbutamol or the use of other drugs or treatments for the prevention of premature delivery. Other medical management may include transfer of the pregnant woman to specialist obstetric services and/or administration of steroid or other medication to promote foetal lung maturation. The present invention would also be useful to confirm that any given pregnancy, at the time of measuring the level of CRH of the woman, should proceed to full term if the level of CRH measured was within normal range. BRIEF DESCRIPTION OF THE DRAWINGS In order that the nature of the present invention may be more clearly understood, preferred forms thereof will be described with reference to the following examples and drawings: Figures 1 a and b shows maternal plasma CRH concentrations throughout midgestation in women whose pregnancies ended in spontaneous preterm labour (n=24) , spontaneous term labour (n=308) , or post-term delivery (n=29) . In Figure la, mean (± s.e.m.) plasma CRH in women delivering at term (points with error bars) was compared with individual samples taken from women delivering preterm (■) or in b, postterm (■) ; Figures 2 a and b provide a graphical representation of regression analysis of the levels shown in Figure 1. Figure 2a shows log linear regression curves fitted to plasma CRH results from the three subject groups. Figure 2b is a non-logarithmic representation of the three regression curves demonstrating the exponential increase of plasma CRH with advancing gestation; and Figure 3 is a comparison of molar concentrations of CRH and CRH-BP in maternal plasma during the final 180 days of gestation in pregnancies ending in spontaneous term labour (37-42 weeks gestation) . BEST METHOD OF CARRYING OUT THE INVENTION Maternal CRH levels can be measured in plasma samples via a radioimmunoassay method that has been described previously(2) . Example 1 The maternal plasma levels of CRH in pregnant women were measured throughout gestation by radioimmunoassay in extracted plasma as previously described (2) and these levels were related to stage of gestation. The results are shown in Figures 1 and 2. Maternal plasma CRH concentrations were measured throughout mid-gestation in women whose pregnancies ended in spontaneous preterm labour (less than 37 weeks gestation, n = 24) , full term labour (37-42 weeks, n = 308), or post-term delivery (induction of labour greater than 41.5 weeks or spontaneous labour greater than 42 weeks, n = 29). In Figures 2a and b the three curves are parallel and the CRH curve is shifted significantly to the left (by 6 weeks) in pregnancies delivering preterm (p 0.05), and significantly to the right (by 2 weeks) in pregnancies delivering post-term (p = 0.02). The median gestational age at delivery was 34 weeks in the preterm group, 40 weeks in the term group and 42 weeks in the post-term group. Each subject provided 1-4 samples (median = 2) which were collected at routine antenatal clinic visits at 4 to 6 week intervals. Gestational age was estimated by ultrasonography in 95% of subjects and by date of the last menstrual period in the remainder. Obstetric outcomes were obtained from a computerised database, and written case notes of all preterm deliveries were reviewed by two clinicians blinded to the CRH results. Women delivered by Caesarean section or after induction of labour are excluded from the analysis, except those already pos -term at the time of delivery. Analysis of parallelism and shift of the regression curves was performed using the method of Kleinbaum et al ^ 3 ^ * Comparison of the molar concentrations of CRH and CRH-BP in maternal plasma during the final 180 days of gestation in pregnancies ending in spontaneous term labour (37 to 42 weeks gestation) is shown in Figure 3. CRH-BP was measured by radioimmunoassay as previously described <4) . Each point represents the mean (± sem) of samples grouped by 10 day intervals calculated retrospectively from the day of delivery (mean of 59 samples at each point) . This analysis includes all samples from the 308 women with spontaneous term delivery prospectively sampled for the present study, and additional samples (collected using identical methodology) from 124 women sampled throughout late pregnancy and parturition for a previously reported study <3) CRH and CRH-BP were measured in duplicate aliquots. CRH and CRH-BP concentrations are significantly different (t-test, p less than 0.002) at all points except at the intersection of the 2 curves, 20 days before delivery. Example 2 In a randomised trial of tocolytic treatment of patients presenting in apparent preterm labour, maternal plasma CRH levels were measured by radioimmunossay in extracted plasma as previously described (2) . The patients were treated with transdermal nitric oxide donating drugs or salbutamol. The results are shown in Table 1. Table l Patient Gestation Length of Basal CRH Gestation Treatment No (weeks) Treatment (pmol/L) extended 1 32 NO(1) * 12 hrs 93.53 4 days 2 33 NO(l) 12 hrs 7.40 8 weeks 3 32 NO(l) 12 hrs 16.76 10 weeks NO(2) Failed 4 30 8.79 11 weeks Sal 15 hrs 5 29 Sal 12 hrs 8.34 10 weeks 6 33 NO(2) 48 hrs 8.80 9 weeks 7 26 Sal 12 hrs 3.19 15 weeks 8 26 Sal 12 hrs 4.88 14 weeks 9 28 Sal 12 hrs 4.72 12 weeks 10 29 Sal 12 hrs 28.45 l day 11 32 NO(2) 48 hrs 12.44 6 weeks 1 Numbers in parenthesis indicate the number of skin patches used. If after 1 hour the first patch had not caused contractions to stop, a second patch was applied. If after a further hour contractions had still not ceased the treatment was recorded as having failed. After failure of NO treatment salbutamol was administered. Patients with significantly elevated CRH (1 and 10) delivered within the next few days inspite of treatment. Patients with lower levels of CRH did not deliver for a number of weeks. The present inventor has shown that the timing of human parturition is influenced from an early stage in pregnancy by a longitudinal maturation process in the foetal-placental unit. The measurement of the maternal plasma CRH concentration (a placental trophoblast product) was utilised as a marker of this process. Plasma samples were obtained prospectively from 485 women during the second and third trimester and the relationship between maternal plasma CRH and the subsequent gestational age at the time of onset of labour was determined. The maternal plasma CRH concentration rose exponentially as pregnancy advanced (Figures 1 and 2), as previously described' 5, 6) . Women delivering prematurely had elevated CRH levels from the earliest stage in pregnancy at which CRH can be measured by the assay used by the inventor. In this group the regression curve of plasma CRH versus gestational age was parallel to that observed in normal pregnancies but was significantly shifted to the left by a magnitude equivalent to the degree of prematurity at the time of delivery. Conversely, in women whose pregnancies continued beyond term the CRH curve was significantly shifted to the right with the magnitude of the shift again corresponding to the extent of post-maturity observed. Previous cross-sectional studies have reported elevated maternal plasma CRH levels at the time of preterm labour (7 - 8) . The present inventor has now shown that the patterns of plasma CRH that are associated with aberrant timing of delivery are established by the end of the first trimester and persist throughout gestation. These data demonstrate the existence of a longitudinal process occurring in the placenta which influences the subsequent timing of delivery. This process may be analogous to a "placental clock" which triggers the onset of parturition at a predetermined time, and that the maternal plasma CRH level is an indicator of the rate of progress towards this event. CRH may act directly as a trigger for the initiation of parturition. Any hypothesis about the action of CRH in pregnancy, however, must include consideration of the recently identified CRH-BP (4) . CRH-BP binds to the hormone in an equimolar ratio and prevents its recognition at the CRH receptor. It is known to be present in the maternal plasma during pregnancy (9) but the relative concentrations of CRH and CRH-BP have not been reported and the bioactivity of placental CRH is therefore unknown. The CRH and CRH-BP concentrations were measured in duplicate aliquots of plasma obtained throughout pregnancy and parturition (Figure 3). CRH-BP was present greatly in excess of CRH until approximately 20 days before spontaneous term delivery. At this time the CRH-BP concentration fell while placental CRH secretion continued to rise exponentially, causing a rapid increase in the bioavailability of free circulating CRH in the final 3 weeks of gestation. There was no detectable difference in plasma CRH-BP levels between the groups of women delivering preterm, at term or post-term (data not shown) . The fall in CRH-BP levels at term is likely to be a consequence of the rising CRH concentration since CRH has been shown to promote rapid clearance of CRH-BP from the circulation (1 °- . There is a striking association between the timing of the increase in CRH bioavailability in late pregnancy and the onset of parturition. Although this does not prove that CRH directly initiates parturition, several lines of evidence suggest that this is likely. CRH receptors have been demonstrated in the myometrium (11) and foetal membranes' 12 -, and CRH has been shown to stimulate the release of prostaglandins from human decidua and amnion in-vitro' 13) and to potentiate the action of oxytocin in inducing myometrial contraction in-vitro' 14■ and in-vivo' 15) . CRH is also present in the amniotic fluid and the foetal circulation where it is capable of stimulating the foetal pituitary-adrenal axis to increase foetal adrenal glucocorticoid secretion, promoting foetal organ maturation' 16* . Finally, prostaglandins and glucocorticoids induced by CRH in turn stimulate further placental CRH secretion' 17"19 - , creating positive feedback loops in the maternal, foetal and amniotic compartments to promote parturition and drive the onset of labour. A critical event in the initiation of human parturition occurs when the maternal plasma CRH level, controlled by the "placental clock", rises to a level sufficient to fully saturate its binding-protein, thereby unmasking CRH bioactivity. This phenomenon is unique to the human species. In no other species does the placenta secrete large amounts of CRH near term and none other than humans have been shown to possess a circulating CRH-BP (20) . Many factors could affect the speed of the placental clock in an individual pregnancy; including genetic predisposition (some women experience repeated premature or post-mature deliveries) , the rate of foetal organ maturation, and pathology in the mother or foetus. The trophoblast is strategically situated at the interface between the maternal and foetal circulations where its function can be influenced by humoral factors originating from either side. Placental CRH secretion is stimulated by inflammatory mediators, cytokines and stress hormones' 19"21 ' and inhibited by the nitric oxide (NO) donors' 22 '. Since NO synthase has been demonstrated in the placenta' 23 ', NO may participate in paracrine regulation of placental CRH expression. The ability to determine at an early stage in pregnancy that the pregnancy may result in preterm or post-term delivery will allow the possibility to initiate medical management of the pregnancy so that a full term delivery may result. The present invention may also be useful to monitor the management of a high risk pregnancy. It has recently been reported that the life expectancy of a given individual may be directly related to the speed of development of the foetus during gestation. Preterm delivery that results from the quicker development of a foetus during pregnancy may result in a shorter life expectancy of the person. Similarly, post-term delivery that results from the slower development of a foetus may result in a longer life expectancy of the person. As the growth of a foetus is affected by the level of CRH during pregnancy, the method of the present invention may also be used to indirectly determine the life expectancy of an individual at an early stage in pregnancy. High levels of CRH indicate the likelihood of premature delivery and thus resulting in a shorter life expectancy. Conversely, low levels of CRH indicate the likelihood of post-mature delivery and thus resulting in a longer life expectancy. INDUSTRIAL APPLICATION The methods of the present invention have application in the management and care of pregnant patients. REFERENCES: (1) In Williams' Obstetrics (eds Cunningham, F G, MacDonald P C, Gant N F, Leveno K J & Gilstrap L C) Vol 19th, 297-361 (Prentice-Hall International, 1993) . (2) Smith R, Cubis J, Brinsmead M W, et al . Psychosomatic Research 4(1) , 53-69 (1990) . (3) Kleinbaum D G, Kupper L L and Muller K E in Applied regression analysis and other multivariable methods (eds Kleinbaum D G, Kupper L L and Muller K E) Vol 2nd, 263-271 (PWS-Kent, Boston, 1988) . (4) Potter E, Behan D P, Fischer W H, Linton E A, Lowry P J and Vale W W. Nature 349, 423-426 (1991) . (5) Campbell E A, Linton E A, Wolfe C D A, Scraggs P R, Jones M T and Lowry P J, J. Clin. Endocrinol . Metab. 64, 1054-1059 (1987) . (6) Sasaki A, Shinkawa 0, Margioris A N, et al. J. Clin. Endocrinol. Metab. 64, 224-229 (1987) . (7) Wolfe C D A, Patel S P, Linton E A, et al. Br. J. Obstet. Gvnecol. 95, 1003-1006 (1988) . (8) Kurki T, Laatikainen T, Salminen-Lappalainen K and Ylikorkala 0. Br. J. Obstet. Gvnecol. 98, 685-691 (1991) . (9) Linton E A, Perkins A V, Woods R J, et al. J. Clin. Endocrinol. Metab. 76, 260-262 (1993) . (10) Woods R J, Grossman A, Saphier P, et al. J. Clin. Endocrinol. Metab. 78, 73-76 (1994) . (11) Hillhouse E W, Grammatopoulos D, Milton N G N and Quartero H W P. J. Clin. Endocrinol. Metab. 76, 736-741 (1993) . (12) Petraglia F, Giardino M, Coukos G, Calza L, Vale W and Genazzani A R. Obstet. Gynecol. 75, 784- 789 (1990) . (13) Jones S A and Challis J R G. Biochem. Biophys. Res. Commun. 159, 192-194 (1989) . (14) Quartero H W P & Fry C H. Placenta 10, 439-443 (1989) . (15) McLean M, Thompson D, Zhang H, Brinsmead M and Smith R. Eur. J Endocrinol 131, 167-172 (1994) . (16) Challis J R G and Hooper S. Bailliere's Clinical Endocrinology and Metabolism 3 No3, 781-793 (1989) . (17) Robinson B G, Emanuel R L, Frim D M & Majzoub J A. Proc. Natl. Acad. Sci. USA 85, 5244-5248 (1988) . (18) Jones S A, Brooks A N and Challis J R. J. Clin. Endocrinol. Metab. 68, 825-830 (1989). (19) Petraglia F, Sutton S & Vale W. Am. J. Obstet. Gynecol. 160, 247-251 (1989). (20) Smith R, Chan E C, Bowman M E, Harewood W J and Phippard A F. J. Clin. Endocrinol. Metab. 76, 1063-1068 (1993) . (21) Petraglia F, Garuti G C, De Ramundo B, Angioni S, Genazzani A R and Bilezikjian L M. Am. J. Obstet. Gynecol. 163, 1307-1312 (1990). (22) Sun K, Smith R & Robinson P J. Basal and KC1 stimulated Corticotropin Releasing Hormone release from human syncytiotrophoblasts is inhibited by sodium nitroprusside. J. Clin. Endocrinol. Metab. in press 1994. (23) Conrad K P, Vill M, McGuire P G, Dail W G and Davis A K. FASEB J. 7, (13) :1269-1276 (1993).

Claims: THE CLAIMS 1. A method of early detection of premature delivery in a pregnant human subject, the method comprising: measuring during the first or second trimester of that pregnancy the maternal level of corticotrophin- releasing hormone (CRH) or of another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species, found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that the delivery will occur sooner than full term if the level of CRH is elevated relative to the normal level of CRH or if the level of the other molecular species deviates from the normal level in a manner indicative of advanced development of the foetal- placental unit. 2. A method of early detection of post-mature delivery in a pregnant human subject comprising: measuring during the first or second trimester of that pregnancy the maternal level of corticotrophin- releasing hormone (CRH) or of another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that the delivery will occur later than full term if the level of CRH is depressed relative to the normal level of CRH or if the level of the other molecular species deviates from the normal level in a manner indicative of retarded development of the foetal- placental unit. 3. A method for determining whether a pregnant human patient experiencing preterm uterine contractions is at risk of delivering prematurely the method comprising: measuring the maternal level of corticotrophin- releasing hormone (CRH) or another molecular species which functions as a marker for the placental clock which reflects development of the foetal-placental unit; comparing the level so obtained with the normal level of CRH or of that other molecular species found in humans having a full term pregnancy and at the same stage of gestation as the pregnant human subject; and determining that delivery is likely to occur prematurely if the level of CRH is elevated relative to the normal level of CRH or if the level of the other molecular species deviates from the normal level in a manner indicative of advanced development of the foetal placental unit. 4. A method according to any one of claims 1 to 3 wherein the measuring of the CRH level is by an immunological method. 5. A method according to claim 4 wherein the immunological method is a radioimmunoassay. 6. A method according to any one of claims l to 3 wherein if a premature or post-mature delivery in a pregnancy of a human subject is predicted, then medical management of the pregnancy is instigated so as to result in an improved outcome for the foetus. 7. A method according to claim 6 wherein the medical management includes the transdermal application of nitric oxide donating drugs for the prevention of premature delivery. 8. A method according to claim 6 wherein the medical management includes transfer of the pregnant woman to specialist obstetric services and/or administration of steroid or other medication to promote foetal lung maturation. 9. A method for confirming that any given pregnancy should proceed to full term the method comprising measuring the maternal level of corticotrophin-releasing hormone (CRH) or another molecular species which functions as a marker for the placental clock which reflects the development of the foetal-placental unit to determine if the level is within normal range. 10. A method for indirectly determining the life expectancy of an individual by measuring levels of CRH in the maternal plasma of the individual's mother while the individual is in utero and determining that life expectancy of the foetus will be short if the level of the CRH is high compared to levels determined in patients delivering full term and at the same stage of gestation as the mother or determining that life expectancy of the foetus will be long if the level of CRH is low compared to levels determined in patients delivering full term and at the same stage of gestation as the mother.

Inventors: SMITH ROGER, SMITH, ROGER
Applicants: SMITH ROGER, UNIV NEWCASTLE, SMITH, ROGER, UNIVERSITY OF NEWCASTLE
Application year: 1995
Main classification: G01N33
IPC codes: G01N33