Handbook of Genetic Counseling/Fetal Hydantoin Syndrome
Fetal Hydantoin Syndrome
- Prenatal hydantoin (dilantin, phenytoin) exposure
- Phenytoin= anticonvulsant first introduced in1938.
- Teratogenic effects were first recognized in 1964.
- Numerous studies have demonstrated increased risk for congenital defects, both major and minor.
- Study conducted from 1985-1992
- 332 newborns exposed to phenytoin (hydantoin, dilantin) during the 1st trimester
- A total of 15 (4.5%) had major birth defects, including:
- Spina bifida
- Broad nasal bridge, wide anterior fontanelle, low hairline, broad alveolar ridge, short neck, hypertelorism, microcephaly, cleft lip/palate, low set ears, epicanthal folds, ptosis, coloboma, coarse scalp hair.
- Small or absent nails, hypoplasia of distal phalanges, altered palmar crease, digital thumb, dislocated hip
- Mild to moderate growth deficiency, usually prenatal in onset
- Occasional borderline to mild mental deficiency. Performance in childhood is usually better than that predicted in infancy
- Cardiovascular (occasional abnormalities):
- Aortic valvular stenosis, coarctation of aorta, PDA, septal defects
- GI (occasional abnormalities):
- Pyloric stenosis, duodenal atresia, anal atresia
- Other (occasional):
- Small nipples that are widely spaced, umbilical and inguinal hernia.
- Risks of delivering a child with congenital defects is 2-3x greater for women taking dilantin than for the general population.
- Increased risk could be caused by epilepsy, the drugs, or a combination of the two. It is thought that the drugs are the causative factor.
- Risks of child having full syndrome is about 10% and the risk for having some of the effects of the disorder is an additional 33%
- Some reports have shown that phenytoin is a transplacental carcinogen. Tumors were reported to occur after in utero exposure to phenytoin in a few cases.
- Phenytoin may induce folic acid deficiency in the epileptic patient by impairing GI absorption or by increasing hepatic metabolism. Therefore, the risk for having a baby with a spinal abnormality is increased.
- Some risk of early hemorrhagic disease of the newborn. Occurs during the 1st 24 hours after birth and can be fatal. Exact mechanism: unknown. Drug is thought to deplete already low levels of fetal vitamin K therefore suppressing the vitamin K-dependent coagulation factors II, VII, IX, and X. Proposed treatment regimen: taking oral vitamin K during last 2 months of pregnancy, C section if difficult labor or trauma is suspected, administering intravenous vitamin K to the newborn in the delivery room (this regimen hasn't been tested in clinical controlled trials, but are logical).
- Risk of not taking phenytoin: pregnant patient can have seizures and can cause the baby to have fetal hypoxia.
- Phenytoin is excreted into breast milk. Milk:plasma ratios range from 0.18 to 0.54.
- Little risk to the infant if maternal levels are kept in the therapeutic range
- Drowsiness and decreased sucking were observed in one infant, no other adverse effects have been reported.
- The American Academy of Pediatrics considers phenytoin to be compatible with breast feeding.
- Briggs GG, Freeman RK, Yaffe SJ. Drugs in Pregnancy and Lactation. 5th edition. Baltimore: Williams & Wilkins.
- Jones KL. Smith's Recognizable Patterns of Human Malformations. 5th edition. W.B. Saunders Company: Philadelphia. 1997.
The information in this outline was last updated in 2002.