In the first trimester of human pregnancy villous cytotrophoblasts are able to differentiate to form either the overlying syncytiotrophoblast layer or, in anchoring villi, extravillous trophoblasts which grow out from the villi and invade into the maternal decidua, acting to both physically attach the placenta to the decidua, and modify the maternal spiral arteries to sustain pregnancy. During the first 10-12 weeks of gestation, extravillous trophoblast plugs block the spiral arteries and prevent maternal blood flow entering the intervillous space, thereby creating an environment of physiological hypoxia in which placental and fetal development occur. As extravillous trophoblasts migrate away from the villus they differentiate from a proliferative to an invasive phenotype. The hypoxic environment of the first trimester is believed to play an important role in the regulation of trophoblast differentiation. However, there is currently a large body of conflicting experimental evidence concerning this topic. This review examines the experimental evidence to date on the role of oxygen in trophoblast differentiation.

BackgroundSleep disturbances in late pregnancy are common. This study aimed to survey sleep problems in third trimester pregnant women and to compare sleep in the pre-pregnancy period with the third trimester.MethodsThird-trimester women (n=650) were sent a postal survey containing questions relating to sleep experience, including perceived sleep quality, sleep difficulties, night waking, sleep environment, snoring, daytime tiredness and daytime napping. Time periods reported on were before pregnancy and in the last week.ResultsRespondents numbered 244 (38%). Before pregnancy, the mean reported duration of night-time sleep was 8.1 (SD 1.1) hours; in the last week this had decreased to 7.5 (SD 1.8) hours (p<.0001). Only 29% rated their sleep quality in the last week as very good or fairly good, compared with 82% rating their sleep this way before the pregnancy. The main reasons for sleeping difficulties were discomfort (67%) and pain (36%). Snoring increased significantly over the course of the pregnancy, with 37% reporting snoring often or every night in the last week. Those with a pre-pregnancy body mass index of greater than 25 were significantly more likely to snore (p=.01). Only 4% of women had an abnormal Epworth Sleepiness Scale score (i.e. >10) prior to pregnancy, whereas in the last week 33% scored in the abnormal range. Likewise, 5% had regularly napped during the daytime before pregnancy, compared with 41% in the last week.ConclusionsSleep problems are common in women in late pregnancy, and increase markedly compared with before pregnancy.

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Key pointsr Fetal behavioural state in healthy late gestation pregnancy is affected by maternal position. r Fetal state 1F is more likely to occur in maternal supine or right lateral positions. r Fetal state 4F is less likely to occur when the woman lies supine or semi-recumbent. r Fetal state change is more likely when the woman is supine or semi-recumbent. r Fetal heart rate variability is affected by maternal position with variability reduced in supine and semi-recumbent positions.Abstract Fetal behavioural states (FBS) are measures of fetal wellbeing. In acute hypoxaemia, the human fetus adapts to a lower oxygen consuming state with changes in the cardiotocograph and reduced fetal activity. Recent studies of late gestation stillbirth described the importance of sleep position in the risk of intrauterine death. We designed this study to assess the effects of different maternal positions on FBS in healthy late gestation pregnancies under controlled conditions. Twenty-nine healthy women had continuous fetal ECG recordings under standardized conditions in four randomly allocated positions, left lateral, right lateral, supine and semi-recumbent. Two blinded observers, assigned fetal states in 5 min blocks. Measures of fetal heart rate variability were calculated from ECG beat to beat data. Compared to state 2F, state 4F was less likely to occur when women were semi-recumbent [odds ratio (OR) = 0.11, 95% confidence interval (95% CI) 0.02, 0.55], and supine (OR = 0.27, 95% CI 0.07, 1.10). State 1F was more likely on the right (OR = 2.36, 95% CI 1.11, 5.04) or supine (OR = 4.99, 95% CI 2.41, 10.43) compared to the left. State change was more likely when the mother was semi-recumbent (OR = 2.17, 95% CI 1.19, 3.95) or supine (OR = 2.67, 95% CI 1.46, 4.85). There was a significant association of maternal position to mean fetal heart rate. The measures of heart rate variability (SDNN and RMSSD) were reduced in both semi-recumbent and supine positions. In healthy late gestation pregnancy, maternal position affects FBS and heart rate variability. These effects are likely fetal adaptations to positions which may produce a mild hypoxic stress. Abbreviations CI, confidence interval; CTG, cardiotocograph; FBS, fetal behavioural state; FHR, fetal heart rate; FHRV, fetal heart rate variability; OR, odds ratio; P aO2 , arterial partial pressure of oxygen; RR interval, interval between successive R waves on the electrocardiograph; RMSSD, root mean square of successive differences (in the RR interval); SDNN, standard deviation of the RR interval.