<unk>  is caused by problems with the development of the nasal cavity and the palate. Development begins with neural crest cells. Frontonasal processes fold, forming nasal placodes (nasal pits). The nasobuccal membrane must rupture in places to form the<unk> . A number of theories exist as to how this developmental process causes<unk> . Risk factors Very few risk factors for<unk>  have been identified. In general,<unk>  is associated with a higher risk of other birth defects. Bilateral<unk>  is more associated than unilateral<unk> . While causes are unknown, both genetic and environmental triggers are suspected. One study suggests that chemicals that act as endocrine disrupters may put an unborn infant at risk. A 2012 epidemiological study looked at atrazine, a commonly used herbicide in the U.S., and found that women who lived in counties in Texas with the highest levels of this chemical being used to treat agricultural crops were 80 times more likely to give birth to infants with<unk>  or stenosis compared to women who lived in the counties with the lowest levels. Another epidemiological report in 2010 found even higher associations between increased incidents of<unk>  and exposure to second-hand-smoke, coffee consumption, high maternal zinc and B-12 intake and exposure to anti-infective urinary tract medications. The anti-thyroid medication methimazole has been associated with the development of<unk>  in rare cases if given during the first trimester of pregnancy.
Choanal atresia
Hypospadias
Duodenal atresia
Intestinal atresia
Gastric atresia
Cloacal exstrophy
Gastroschisis
Diaschisis