Is there an increased rate of anencephaly in twins?

Background: The Israeli Ministry of Health reported an increased rate of twin pregnancies among all cases locally diagnosed as having open neural tube defects. The current study aimed to evaluate whether the etiology of this phenomenon could be attributed either to the twinning or to the mode of conception. Methods: Women admitted to our hospital between January 1997 and July 2004 for termination of pregnancy because of severe fetal abnormality enrolled into this retrospective case series study. They were further subdivided according to mode of conception (spontaneous, in vitro fertilization (IVF) or intracytoplasmic sperm injection (IVF-ICSI) pregnancies). Results: Three-hundred and eighty consecutive pregnancies, of which 340 (89%) were singletons, participated in our study. Anencephaly was diagnosed in 26 cases: 19 singletons and 7 twins. In the entire twin population, they were all dichorionic twins and only one co-twin was affected. Five of the twins were conceived by IVF-ICSI. All the anencephalic IVF-ICSI twins had normal karyotypes. All IVF-ICSI study women had taken folic acid 400 mcg/day 3 months before conception and throughout the first trimester of pregnancy. In order to find out the cause of the high rate of anencephaly found in IVF-ICSI pregnancies (33.3%), either the twinning or the IVF-ICSI process, a logistic regression analysis was used. A significant correlation was found only between anencephaly and twinning (p = 0.001, CI = 1.86-12.63), with a risk ratio of 4.85. Conclusions: Our case series data suggest a comparatively higher rate of anencephaly in IVF-ICSI pregnancy secondary to twinning and not because of the assisted reproductive technology. It is suggested that larger epidemiologic studies are conducted to validate our preliminary results.