Objectives To determine the perinatal outcome of fetuses who had birthweights less than that expected from early third trimester ultrasound scanning. Design Retrospective estimation of centile fetal weight at early third trimester ultrasound scanning compared with actual centile birthweight corrected for gestational age, parity and sex. Setting Teaching Hospital Obstetric Unit, London. Subjects 197 unselected women with singleton cephalic pregnancies who were delivered at term in our unit between October 1989 and May 1990. Main outcome measures CTG abnormality, need for fetal blood sampling in labour, meconium‐staining of the amniotic fluid, mode of delivery, Apgar scores at 1 and 5 min, need for transfer of baby to neonatal unit, and need for neonatal intubation of the neonate at delivery. Results An actual birthweight >5% less than the birthweight estimated from ultrasound scanning identified 44 babies (22%) with an increased risk of CTG abnormalities (χ2= 8.38, P <0.0025; Odds ratio (OR) = 2.54; 95% CI1 1.6 to 4.78) and need for operative delivery (x= 5.81, P <0.0125; OR = 1.94; 95% CI 1.15 to 3.27), when compared with the remainder of the sample. Overall 14 (32%) of this group had birth‐weights above the 50th centile. A group of 44 babies selected as being the smallest for gestational age, without reference to growth pattern, had a similar excess morbidity. (All this group had birthweights below the 39th centile.) Conclusions This study supports the hypothesis that in‐utero fetal growth pattern is as important for perinatal outcome as being small for gestational age per se.

Objective To assess the relation between peak active (above baseline) head‐to‐cervix force (paHCF) and peak active (above baseline) intrauterine pressure (paIUP) in labour, and to compare the relation between labours progressing well and ending in vaginal delivery and those labours progressing slowly and ending in caesarean section. Design Prospective observational study. Setting The labour ward of a London teaching hospital. Participants Forty women in labour who agreed to have an experimental head‐to‐cervix force probe and an intrauterine pressure catheter inserted. Results The relation was linear, with a correlation coefficient which ranged from 0.012 to 0.885 (mean value 0.438). The closeness of the relation did not correlate with the rate of cervical dilatation (r = 00192, P= 0.574) or the mode of delivery (r = 0.215, P= 0.183). However, in women who progressed well to a vaginal delivery, the mean slope of the paHCF to paIUP regression line was 0.72, significantly steeper than in women who progressed slowly and required delivery by caesarean section (mean slope = 0.45, t = 2.31, P= 0.02). Mean paIUPs were significantly higher in women progressing well and achieving a vaginal delivery than in those progressing slowly and requiring caesarean section (45.3 mmHg SD 7.5 vs 38.4 mmHg SD11.4, t = 2.31, P= 0.02), but the overlap between the two groups was considerable. However, in keeping with their steeper paHCF/paIUP slope, women progressing well to a vaginal delivery had substantially higher head‐to‐cervix forces (46.4 gWt SD 11.8 vs 28.3 gWt SD 8.2, t = 5.22, P < 0.00001) than those progressing slowly and requiring caesarean section, and there was much less overlap between paHCF than paIUP. This resulted in paHCF being a much better discriminating variable than paIUP for mode of delivery. Conclusions The relation between paHCF and paIUP is linear, but there is a wide variation in the degree of correlation between one woman and another. Women with a steep slope of paHCF relative to paIUP are more likely to achieve a high mean paHCF, progress rapidly in labour and achieve a vaginal delivery than women with a flap slope, although mean paIUPs do not differ substantially between the two groups. The level of paHCF was substantially better than cervical dilatation rate at predicting mode of delivery. These results suggest that head‐to‐cervix force is sensitive to factors determining mode of delivery which are not reflected in either the level of uterine activity as measured by intrauterine pressure, or cervical compliance as measured by cervical dilatation rates.

Objective To investigate the relation between the rise in intrauterine pressure and rise in fetal head to cervix force in normal, slow and induced labour. Design Prospective observational study. Setting The labour ward of a London teaching hospital. Participants Forty patients were recruited from the antenatal clinic and labour ward of a West London Hospital. Five had normal onset and progression of labour, 14 had slow progression of labour and 21 had induced onset of labour. Method Intrauterine pressure and head‐to‐cervix force was measured simultaneously using an intrauterine pressure catheter and a specially designed four sensor head‐to‐cervix force probe. Results For each contraction of each labour, scattergrams of force by pressure were plotted. Three patterns were observed. When the rise in pressure preceded the rise in force, a positive ‘loop’ was generated. When the rise in pressure and force occurred simultaneously a linear pattern was generated (a neutral ‘loop’). When the rise in pressure lags the rise in force, a negative ‘loop’ was generated. In normally progressive labour the distribution of loops was 291%, 22.6% and 48‐3 %, respectively, in slow labour the distribution was 26.1 %, 14.1 % and 59.8 % and in induced labour the distribution was 33.8 %, 14.4% and 51.8 %. These distributions were not statistically different. However, a higher proportion of negative loops was observed in labours augmented with oxytocin compared to those receiving no oxytocin (MW‐U = 87, P= 0.036). No differences were observed comparing parity, use of PGE2, epidural analgesia, or mode of delivery. Contraction frequency (number/10 minutes) was inversely correlated to the percentage of negative loops (r8= 0.34, P= 0.033) and positively correlated with percentage of positive loops (r8= 0.36, P= 0.027). Conclusions This is the first report of the temporal relation between intrauterine pressure and head‐to‐cervix force in labour. The most common pattern is that the rise in pressure lags the rise in force, suggesting that a seal has to be created between the fetal head and cervix before a rise in pressure can occur. When oxytocin is given in labour, a higher proportion of loops are negative indicating that there is poor application of the fetal head and cervix in a greater proportion of contractions.

The factors that determine the circulating levels of relaxin during pregnancy have been investigated by comparing the plasma levels of relaxin throughout pregnancy in women who became pregnant spontaneously (singleton, n = 240) or following superovulation (singleton and multifetal pregnancies (two to ten conceptuses), n = 83). Some of the women with multifetal pregnancies underwent selective fetal reduction to twin pregnancies. Relaxin levels were higher at 7-34 weeks of gestation in singleton pregnancies achieved following superovulation when compared with levels in spontaneously conceived singleton pregnancies (p < 0.05-0.001). In samples obtained between 10 and 12 weeks of gestation (before fetal reduction for the multifetal pregnancies), plasma relaxin levels correlated with fetal number (r = 0.526, P = 0.0001). Reduction in fetal number to a twin pregnancy did not alter relaxin levels. These data suggest that the circulating levels of relaxin throughout pregnancy are determined during the cycle of conception by gonadotrophin stimulation, and within the first 10 weeks of pregnancy by the luteotrophic stimulus from the conceptus. Furthermore, once corpus luteum synthesis of relaxin is established, then reduction in the luteotrophic stimulus does not appear to affect it.