Is there a seasonal variation in the incidence of potentially folate sensitive fetal malformations?

There have been conflicting reports on the incidence of gastroschisis and its seasonal variation. To evaluate the existence of a seasonal variation in the incidence of gastroschisis and spina bifida in our patients a retrospective database analysis was conducted.

Methods and Materials: Second trimester pregnancy screening was performed on 8031 patients between October 2001 und March 2005 with files in our database. Patients were evaluated throughout the year separately for their expected date of delivery during the summer months (April- September) and the winter months (October – March).

Results: We have diagnosed 17 foetuses having gastroschisis with a mean gestational age at diagnosis of 24 weeks (range 11–33). In other 45 fetuses spina bifida was found. The expected date of birth of fetuses with gastroschisis was significantly more common (p<0,05 during the winter months (N=11) than during summer months (N=6). For the incidence of spina bifida no seasonal variation was found (23 vs. 22).

Conclusions: There is a seasonal variation in the risk of gastroschisis depending on the estimated date of birth. But there is no seasonal variation in the incidence of spina bifida.