BMC Public Health 2007, 7:268 http://www.biomedcentral.com/1471-2458/7/268 mation from the women's maternity case notes that they carry with them, and by clinical records of Kuopio Univer- sity Hospital. Gestational age of 42+0 weeks or more was used as definition for prolonged pregnancies. Low hemo- globin was defined as under 100 g/l in the third trimester of pregnancy. Pre-eclampsia was defined as repeated blood pressure measurement exceeding 149/90 mmHg with proteinuria exceeding 0.5 g/day. Chorio-amnionitis, placental abruption or placenta previa were registered when these obstetric diagnoses were set during the hospi- tal stay. Abnormal CTG was recorded to the database by obstetricians. Meconium staining of amniotic fluid during delivery was marked in the delivery reports and to the database by midwives. Preterm birth was delivery before 37 weeks of gestation. Estimation of gestational age was based on menstrual his- tory and ascertained by measuring fetal crown-rump length by ultrasonography in approximately 95% of cases at 10 to 12 weeks of pregnancy. Infants were considered small for gestational age (SGA) when the age- and sex- adjusted birth weight was below the tenth percentile according to the normal tables for our population [15], and of low birth weight (LBW) when it was less than 2500 g. The mode of delivery was registered to the database as: spontaneous, instrumental or cesarean section. Apgar scores were given mainly by midwifes in uncomplicated deliveries and by pediatricians, when consulted, and were considered low when the scores were less than 7. The pH limit used for fetal acidosis was 7.15 at birth in the umbil- ical vein. Abnormal CTG was recorded to the database by obstetricians. The admission rate to the neonatal intensive care unit (NICU) was recorded as infants requiring more than 24 hours surveillance. Neonates needing only obser- vation are also treated in the NICU in our hospital. Fetal death was defined as intrauterine death of a fetus over 22 weeks of gestational age or over 500 g weight and neonatal death as death during the first seven days after birth. If a subject had two abnormalities, such as LBW and preterm delivery, each was considered an independent outcome and the subject was included in both categories. The validity of the data has manually been checked for some specific pregnancy complications, such as perinatal deaths, velamentous umbilical insertions, umbilical cord knots and placental abruptions. Statistical differences between the subjects and the refer- ence group were evaluated by using Chi-square tests (dichotomous variables), and Fisher's exact test was applied when the minimal estimated expected value was less than five. A value of p < 0.05 was considered statisti- cally significant. Continuous variables were analyzed by using two-tailed, pooled t tests. Logistic regression analy- sis controlling for all clinically significant possible con- founding factors was performed (SAS for Windows, SAS release 8 statistical package). The logistic regression mod- els included: age under 18 y, age over 35 y, unmarried sta- tus, smoking during pregnancy, using alcohol during pregnancy, educational level, primiparity, multiparity, prolonged gravidity, chronic illness and diabetes. Confi- dence intervals were evaluated at 95%. Results Of the obstetric population of singletons without major anomalies, 270 (1.0%) had no antenatal care visits, 207 (0.77%) had 1–5 visits, and 23137 (85.8%) had an aver- age number (6–18) of antenatal care visits. The differ- ences between the study groups and the reference group in incidence of birth outside hospital were statistically signif- icant (P < 0.025 for under-attenders and P < 0.001 for non-attenders), although the numbers were very small: In the group of 6–18 antenatal care visits 14 (0.09%) infants were born outside hospital, in the group of no antenatal care there were 5 (1.85%) and in the group of 1–5 visits one (0.97%). No difference in ages of the women in the study groups and in the reference group was found: the mean age (± standard deviation) of the women who had 6–18 antenatal visits being 28.7 ± 5.3 y, vs. 28.8 ± 6.5 y (p = 0.85) in the non-attenders and 28.13 ± 6.7 y (p = 0.10) in the under-attenders. The youngest mother in this study was 14 y and the oldest 52 y. The study population was ethnically homogeneous. Non-attenders and under-attenders of antenatal care were statistically significantly more often unmarried, smokers, and less often highly educated (Table 1.). Young age was more common in the group of non-attenders than aver- age. Moreover, grand multiparity was more common in under-attenders than on average, as was alcohol use dur- ing pregnancy. Furthermore, the pregnancies of non- attenders and under-attenders of antenatal care were sig- nificantly more often (p < 0.001) complicated by placen- tal abruption (4.44% and 6.28% vs. 0.70%, respectively) or chorio-amnionitis (4.83% and 9.66% vs. 1.37%, respectively), but no differences were found as regards other pregnancy complications. The mean birth weight (± standard deviation) of new- borns was 3503 ± 617 g in the women with 6–18 antena- tal visits, 3014 ± 1033 g in the non-attenders and 2704 ± 1156 g in the under-attenders. Accordingly, the newborns of non-attenders and under-attenders of antenatal care weighed 489 and 799 g less, respectively, than the new- borns of mothers with an average number of antenatal vis- its, these differences being statistically significant (p < 0.0001). 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