Perinatal Risk Factors: With special reference to Intrauterine Growth Retardation and Neonatal Respiratory Adaptation
Authors: Wennergren Margareta 
Published: December 2009

Intrauterine growth retardation (IUGR) and neonatal respiratory disorders (RD) are two dominating problems in perinatal medicine. The aims of this study were to analyze the possibilities of selecting groups of pregnant women with increased risk of either problem, to analyze the relationship between IUGR and neonatal respiratory disorders and to evaluate the influence on neonatal respiratory adaptation of different events during delivery. For these purposes epidemiological methods were mainly used but in paper V an animal model was applied.

In the whole population of pregnant women attending the antenatal clinic of the department during a six month period the items which had the best discriminating power between normal and IUGR pregnancies were selected. These eight items (previous infants ≤2500 g, hypertension, kidney diseases, smoking, bleeding with or without uterine contractions, insufficient increase of weight, girth or fundal height) were used as a scoring system. With a risk population of 7%, all IUGR cases were included. The IUGR infants constituted 34% of the risk group.

For one year all newborns of mothers living in Göteborg were screened prospectively for signs of respiratory disorders. It was not possible to indicate antenatally pregnancies with increased risks of neonatal respiratory disturbances. Preterm small for gestational age (SGA) infants were found to have the same risk of RD as non‐SGA infants. Full term SGA infants had a higher incidence of RD, which could not be explained by their higher incidence of cesarean sections (CS) and low Apgar scores.

In preterm infants and in full term infants after CS the relation between rupture‐delivery interval and risk for RD was “u‐shaped”. There was a higher incidence of RD if delivery was immediately at rupture than a few hours up to 36 h later. After more than 36 h the risk increased again. Consequently there seems to be no advantage in postponing delivery more than 36 h after ROM.

The impact of CTG (cardiotocography) pattern on RD during delivery, was analyzed in two subgroups of infants (≥ 37 weeks, delivered by CS). Infants with ominous CTG patterns were unexpectedly found to have a reduced incidence of RD, 6% compared to 21% in infants with normal patterns. A possible explanation could be that “intrauterine stress” might exert a positive effect on neonatal respiratory adaptation.

Low Apgar score was an important risk factor for RD in full term infants and infants 33–36 weeks of gestation. In immature infants (le;32 weeks) a low Apgar score did not further increase the risk of RD, and after CS the importance of low Apgar score was reduced. No single component in the Apgar score was predictive of RD, but “low vitality” in general seems decisive.

Finally, in an animal model with newborn rabbits and guinea pigs the importance of an excitatory influence from the central chemoreceptors on the establishment and maintenance of a regular breathing at birth was demonstrated. It was also shown that the inhibition of breathing seen in newborns after pethidine has been given as obstetric analgesia, might be elicited via inhibition of the central chemoreceptor system.