Gastroschisis in on the increase. It's a congenital anomaly where the abdomial wall fails to form properly, so the baby is born with its intestines more or less open to the world. The defect can be corrected with surgery, but it's a devastating condition for the parents to endure.
About 10 years ago, researchers in Wales were investigating a cluster of gastroschisis and formed the view that the mothers of affected babies (a) were thinner and (b) drank more alcohol than other mothers. So congratulations to them for sticking with the subject and carrying out a formal study of all affected births (124 of them) in about half of the English population over a 3 year period.
They picked a clean group to study - pure gastroschisis not associated with any other anomaly or syndrome.
Note the use of different data sources - Body Mass Index for example from antenatal records but much else from household interview. The diet question was very simple - 'How often do you typically eat meat / fruit / fish etc' . Notice that the controls were taken from the antenatal clinic attended by the case. This inevitably means that they were matched for 'local way of life', which may mean a whole load of relevant things we can't measure.
The end result was that a higher intake of fruit veg protects against gastroschisis and smoking is (of course) not good. Which leaves the increase in birth prevalence a mystery, to my mind. Smoking in England and Wales is not on the increase, consumption of fruit and veg is not declining. I guess there may be a vulnerable (genetically?) subgroup in whom smoking is increasing and / or diet worsening. Still many questions to answer.