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Genetic counseling: Fetal Hydantoin Syndrome

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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:
      • Cardiovascular
      • Spina bifida
      • Hypospadias

Clinical FeaturesEdit

  • Craniofacies:
    • 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.
  • Limbs:
    • Small or absent nails, hypoplasia of distal phalanges, altered palmar crease, digital thumb, dislocated hip
  • Growth:
    • Mild to moderate growth deficiency, usually prenatal in onset
  • Performance:
    • 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.

Breast FeedingEdit

  • 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.

This material has been imported fom the wikibook "Genetic counseling"[] under the GNU Free Documentation License.

Heckert GNU white Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License."

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