Tobacco smoking and twinning

In a case-control study an association was found between mothers' smoking habits and the frequency of dizygotic twinning. As cases were included all twins born in Denmark in 1984 and 1985. A random sample of 1.5% of mothers to singletons, born in the same period were selected as controls. Only live-borns, conceived after no hormonal treatment, were included in the study. The finding may be due to the well-known anti-estrogen effect of smoking.

Maternal age and parity as predictors of human twinning

A case-control study was conducted to evaluate the association between maternal age and parity and dizygotic (DZ) and monozygotic (MZ) twinning, respectively. Mothers of all twins born alive in Denmark in 1984 or 1985 were included into the study as cases, and a random sample of mothers of singletons were controls. Data on maternal age at delivery and number of previous births were collected from the Danish Medical Birth Register. By means of logistic regression analysis, a significant and positive association was found between maternal age and DZ twinning, and a significant and negative association between parity and MZ twinning. No association was found for parity and DZ twinning, nor for maternal age and MZ twinning. The study suggests that human MZ twinning has predictors too, as has DZ twinning. The finding has implications for zygosity classification in future twin research.

Coital frequency and twinning

In a comparative study to enquire whether parents of twins, especially of dizygotic twins, have a higher frequency of sexual intercourse than parents of singleton infants, data on sociodemographic status, coital frequency and other variables were collected using a postal questionnaire. Parents of all twins born alive in Denmark in 1984 or 1985 were included as cases and a random sample of parents of singleton infants born in the same period were controls. No evidence of any difference in coital frequency was found between parents of twins (neither dizygotic twins nor monozygotic) and parents of singleton infants.

Evaluation of zygosity diagnosis in twin pairs below age seven by means of a mailed questionnaire

The mothers of a consecutive series of 125 same sexed pairs of twins aged 6 months to 6 1/2 years completed a mailed questionnaire concerning the physical similarity of the twin partners. Zygosity diagnoses were first determined blindly on the basis of the answers given by the mothers, who did not know the result of the blood group test when fulfilling the questionnaire. Next, the results were compared with the zygosity determination based on examination of erythrocyte-, serum- and enzyme-groups. It turned out that a few simple questions distinguished well enough between MZ and DZ pairs, with a frequency of misclassification of 4%, leaving 5% as unclassifiable. It is concluded that twin zygosity can be estimated by a simple questionnaire with sufficient accuracy even in very young twin pairs. This has relevant implications for more extensive twin studies where the use of a wide spectrum of serological characters would imply too high expenses.

Menstrual characteristics of mothers of twins

The menarcheal age and frequency of menstrual disorders in mothers of dizygotic (DZ) and monozygotic (MZ) twins born in Denmark in 1984 or 1985 were compared with a control sample of mothers of singleton infants born in the same period. Compared to control mothers, mothers of DZ twins had a lower menarcheal age and a lower frequency of menstrual irregularities--menstrual cycles exceeding 5 weeks duration, varying length of menstrual cycles and episodes of menostasia. Mothers of MZ twins had a higher frequency of intermenstrual bleeding compared to mothers of singletons. All results were adjusted for maternal age and parity. The findings are relevant to the interpretation of aetiological factors leading to twin births and support the hypothesis of differences in sex hormone activity of the mothers of DZ twins in comparison with other women.

[Breech presentation deliveries]

A total of 5,519 consecutive single deliveries at term were analysed for maternal and foetal factors associated with breech presentation (UK). The protocol in this department for breech deliveries which permits vaginal delivery of foetuses estimated to be between 2,400 and 3,800 g in cases where the pelvis was considered to be clinically normal, was also evaluated. Breech presentation was found in 173 cases. In 102 of these circumstances were present which permitted trial of vaginal delivery. Seventy-seven were delivered vaginally. An increased frequency of low Apgar scores (less than 8) after one minute was demonstrated among infants delivered vaginally in the breech presentation on comparison with infants delivered by Caesarean section, whereas low scoring after five minutes occurred with the same frequency. One infant died during delivery. Follow-up of infants delivered in breech presentation (mean period of observation two years) showed developmental disturbances in three of the vaginally delivered infants and in five of those delivered abdominally. Two of the infants delivered abdominally had severe cerebral paresis and psychomotor retardation without evidence of intrauterine or severe neonatal asphyxia. On comparison with the population delivered in cephalic presentation (HST), significantly increased frequencies of primiparity and light-for-dates infants were found in the breech presentations. Low Apgar score after one minute was significantly more frequent in breech presentations while low Apgar scoring after five minutes occurred with the same frequency. The perinatal mortality rates in breech and cephalic presentations were 17.3 and 4.7 per 1,000 respectively. Following correction for lethal malformations, the rates were 5.8 and 3.8 per 1,000, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)