Regulation of self-renewal and differentiation in the Drosophila nervous system.

Stem cells can divide symmetrically to generate two similar daughter cells and expand the stem cell pool or asymmetrically to self-renew and generate differentiating daughter cells. The proper balance between symmetric and asymmetric division is critical for the generation and subsequent repair of tissues. Furthermore, unregulated stem cell division has been shown to result in tumorous overgrowth. The Drosophila nervous system has proved to be a fruitful model system for studying the biology of neural stem cell division and uncovering the molecular mechanisms that, when disrupted, can lead to tumor formation. We are using the Drosophila embryonic and larval nervous systems as models to study the regulation of symmetric and asymmetric stem cell division.

Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history.

OBJECTIVES: To examine the feasibility of introducing routine measurement of cervical length at 23 weeks of gestation, to establish the distribution of cervical lengths in a routine population of singleton pregnancies and to examine the relation between cervical length and demographic characteristics and previous obstetric history. METHODS: Cervical length was measured by transvaginal sonography at 23 weeks of gestation in women with singleton pregnancies attending for routine antenatal care. The distribution of cervical lengths was established and the significance of differences in median cervical length between subgroups according to maternal age, ethnic origin, maternal ponderal index, cigarette smoking, alcohol drinking, drug abuse and previous obstetric history was calculated. In addition, 100 women were asked to complete a questionnaire aimed to assess the degree of discomfort, pain or embarrassment caused by the scan. In 100 pregnancies, cervical length was measured in each patient by two of four operators to determine intraobserver and interobserver variabilities. RESULTS: During the study period, 2702 (80%) of the 3358 women attending for a 23-week scan agreed to participate in the study and, in all cases, the cervical length was measured successfully. The median cervical length was 38 mm and in 1.6% of cases the length was 15 mm or less. More than 90% of the women reported that the procedure was associated with no or only mild discomfort and embarrassment, whilst 85% found the ultrasound scan to be equally or less uncomfortable than a speculum examination. Measurement of cervical length was highly reproducible and, on 95% of occasions, the difference between two measurements by the same observer and by two observers was < or = 3.5 mm and < or = 4.2 mm, respectively. Cervical length was significantly shorter in women of Afro-Caribbean origin compared to Caucasians, those aged less than 20 years, those with a low ponderal index, those with a history of previous miscarriage or preterm delivery and in drug abusers. CONCLUSIONS: Transvaginal sonographic measurement of cervical length is highly reproducible and it is associated with a minimal degree of discomfort to the patients. At 23 weeks, the median cervical length is 38 mm and, in 1.6% of the population, the length is 15 mm or less. There is an association between cervical length and demographic characteristics and previous obstetric history.

Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery.

OBJECTIVE: To examine the potential value of routine measurement of cervical length in singleton pregnancies at 23 weeks of gestation in the prediction of the risk for early spontaneous preterm delivery. METHODS: Cervical length was measured by sonography at 23 weeks in 2567 singleton pregnancies in women attending for routine antenatal care. In 43 women, the length was < or = 15 mm and 21 of these were managed expectantly, whereas in 22 cases a cervical cerclage was placed. In the pregnancies that were managed expectantly, the relation between cervical length and preterm delivery was examined and the risk of spontaneous delivery at < or = 32 weeks was estimated. RESULTS: Cervical length at 23 weeks was < or = 15 mm in 1.7% of cases; this group contained 86%, 58% and 20% of pregnancies that delivered spontaneously at < or = 28, < or = 32 and < or = 36 weeks, respectively. The risk for delivery at < or = 32 weeks decreased from 78% at a cervical length of 5 mm to 4% at 15 mm and 0.5% at 50 mm. CONCLUSIONS: Cervical length at 23 weeks is < or = 15 mm in < 2% of the population; this group contains about 90% and 60% of the women delivering at < or = 28 and < or = 32 weeks, respectively. Measurement of cervical length provides accurate prediction of risk for early preterm delivery.

Detection of sex chromosome abnormalities by nuchal translucency screening at 10-14 weeks.

At 10-14 weeks of gestation more than 80 per cent of fetuses affected by trisomy 21 can be detected by a screening programme based on a combination of maternal age and fetal nuchal translucency thickness (NT). The screen positive group in such a programme also identifies fetuses with sex chromosome abnormalities. In this ongoing multicentre screening study, involving 61,972 singleton pregnancies, 53 cases of sex chromosome abnormalities were identified. The fetal NT was above the 95th centile in 87.9 per cent of the 33 cases with 45,XO, and in 40 per cent of the 20 cases with 47,XXX, 47,XYY or 47,XXX. However, it was estimated that at 12 weeks of gestation our population would contain 42 cases with 45,XO and 104 cases with 47,XXY, 47,XYY or 47,XXX. Since the rate of intra-uterine lethality, between 12 and 40 weeks of gestation, is about 65 per cent for 45,XO and four per cent for 47,XXY, 47,XYY or 47,XXX, the respective number of livebirths with these chromosomal abnormalities would have been 15 and 100, respectively, without prenatal diagnosis. Assuming that all intra-uterine deaths are from those with increased NT, screening for trisomy 21 by maternal age and fetal NT would have identified only 20 per cent of potential livebirths in the 45,XO group and nine per cent of those with 47,XXY, 47,XYY or 47,XXX.