The possibility that specific environmental factors such as smoking and estrogen use modify the genetic influences (gene–environment interaction) on bone mineral density (BMD) has not been explored in genetic epidemiological studies such as twin studies. The aim of this study was to look for evidence of gene–environment interaction in BMD determination by analyzing data collected on a large number of healthy female twins. BMD of the hip, distal forearm and lumbar spine were measured by dual-energy X-ray absorptiometry on 287 identical and 265 nonidentical volunteer female twin pairs. The environmental factors examined were hormone replacement therapy (HRT) and smoking. In genetic modeling analysis using path analysis, there was evidence of ‘HRT-specific’ genetic component of BMD variance at the forearm (50% of total variance) but not at the hip. At the lumbar spine the magnitude of the genetic component of variance in HRT users (> 60-month HRT use) was less than the genetic component of variance for little or no exposure to HRT (48% vs. 84%). There was no evidence of gene–environment interaction for smoking. The main evidence for gene–environment interaction was the finding that forearm BMD variance was influenced by a significant HRT-specific genetic component. There was also evidence that in HRT users, the genetic component of total variance for lumbar BMD was lower.

Our aim was to evaluate the ability of prenatal ultrasound scans to predict fetal growth discordance, and to examine the correlation between fetal weight estimated by ultrasound with actual birthweight in twin pregnancies. The study consisted of 221 twin pregnancies with ultrasound fetal weight estimates based on Hadlock's 4 parameter formula. Prediction of intertwin birthweight discordance was examined at 4 different intervals between ultrasound examination and delivery (0–7 days, n = 96; 8–14 days, n = 66; 15–21 days, n = 58; 22–28 days, n = 59 pregnancies), with a total of 279 ultrasound examinations. Birthweight discordance was considered as a difference of 20% or greater. The correlation between fetal weight estimated between 0 and 7 days and actual birthweight was calculated by intraclass correlation coefficient. The predictive values for intertwin discordance of 20% or more in the 0 to 7 days group were: sensitivity = 93.6%, specificity = 79.4%, positive predictive value = 89.2%, negative predictive value = 87.1% and accuracy = 88.6%. In the groups with scans carried out between 8 and 14 days, 15 and 21 days, and 22 and 28 days, the sensitivity and accuracy values were 95.8% and 84.9%, 95.6% and 84.5%, 90.9% and 84.8%, respectively. Fetal growth discordance in twins can be accurately predicted by ultrasound examination performed up to 28 days before birth. There is a good correlation between fetal weight estimated between 0 and 7 days and actual birthweight.

Fetal death in a twin conception during second and third trimester is associated with increased risk of cerebral injury in the surviving twin. The aim of this study is to test the hypothesis that even early fetal losses as a ‘vanishing’ twin may be associated with an increased risk of cerebral impairment in the surviving twin. The study population comprised 362 pregnant women attending Liverpool Women's Hospital recruited between 1999 and 2001. Women were classified according to the first ultrasound scan into 3 groups: vanishing twin, twin and singleton. The vanishing twin group was further subdivided into ‘definite’ and ‘probable’. Children from these pregnancies were assessed at 1 year of age for their development and neurological function using the Griffiths Mental and Developmental Scales and Optimality score. Children from 229 pregnancies (63.2%) attended the assessment. Information on children from a further 21 (5.8%) pregnancies was obtained through a review of hospital records. Cerebral impairment was found in 2 children from the vanishing twin group, 2 from the twin group and none from the singleton group. When cases with definite vanishing twin are considered there is a significant difference between the vanishing twin and singleton group (relative risk 6.1; 95% confidence interval 1.5–8.3; p = .03). An additional study with an increased sample size would enable a more robust conclusion.

Early loss of one fetus in a multiple gestation as a ‘vanishing’ twin is a well recognized phenomenon. It is uncertain whether this has an impact on the development of the surviving co-twin. The aim of this study is to compare the development of singletons, twins and the surviving co-twins of a vanishing twin. The 324 children born to 229 women who were recruited into the study between 1999 and 2001 formed the study population. Children were assessed at 1 year of age with Griffiths Mental and Developmental Scales. A neurological examination was performed using an optimality score to exclude those with severe neurodisability. Three hundred and five children (92 singletons, 180 twins and 33 survivors with a vanishing twin) were included. The sub- and general quotient scores in singletons and surviving co-twins of a vanishing twin did not differ significantly. Twins had significantly lower scores than singletons in all areas of development and were more likely to be born early with lower birthweights. Following adjustment for gestation and birthweight, the difference between the two groups was nullified suggesting that the slower development of twins is related to their prematurity and lower birthweight.

This case report demonstrates the use of ultrasound and doppler flow in the management of mono-amniotic monochorionic (M/M) twins. M/M twinning is a rare but significant event. It is associated with high rates of fetal mortality, most commonly cited at anywhere from between 30% and 70%. A common cause of death is cord entanglement. The case presented is that of a 19-year-old gravida 1 at 30 weeks with M/M twins in which multiple cord knots were found by ultrasound color doppler flow after variable fetal heart rate decelerations occurred. This prompted a decision for immediate cesarean delivery with normal fetal outcomes. Improvements in perinatal imaging systems are therefore beneficial in the management of M/M twins.

A 2-year study involving macroscopic examination of twin placentae was conducted at the Korle Bu Teaching Hospital in Accra, Ghana to determine the proportions of the various types of twin placentation, cord insertions and number of cord vessels and their relationships. Of 765 twin-pair placentae examined, 398 (52%, 95% confidence interval [CI] 48.4%–55.6%) had fused dichorionic, 247 (32.3%, 95% CI 29.0%–35.7%) had separate dichorionic, and 119 (15.6%, 95% CI 13.1%–18.4%) had monochorionic diamniotic placentae; only one (0.1%, 95% CI 0.0%–0.8%) had monochorionic monoamniotic placentation. Of 1529 cords whose insertion could be determined, 1285 (84%) had disc, 172 (11.2%) marginal and 72 (4.7%) velamentous insertions. Only 10 (0.65%) cords had two vessels (i.e., single umbilical artery). Abnormal cord insertions (marginal and velamentous) were significantly more likely to occur in monochorionic than in dichorionic placentation (odds ratio [OR] 3.56, 95% CI 2.62–4.84), and in two-vessel than in three-vessel cords (OR 5.79, 95% CI 1.44–24.5). The prevalence of two-vessel cord in monochorionic was not significantly different from that in dichorionic placentation (OR = 0.60, 95% CI 0.10–2.67). Zygosity could be determined in 53.3% of twins from placental examination and babies' sex-pair combinations. In conclusion the most common twin placentation in Ghana is fused dichorionic. Abnormal cord insertion is more common in monochorionic than dichorionic placentation. Monoamniotic twins and single umbilical artery are less common than have been reported in other centers. Modern methods of DNA analysis are needed to establish zygosity in almost half of twin pairs.