Genetic disorders, such as
Down syndrome or
cystic fibrosis, and birth defects occur more
frequently in multiple pregnancies than in pregnancies with one fetus. A group
of deformities of the ankles and/or feet (club foot) is an example of a birth
defect seen more commonly in multiple pregnancy.
disorders and birth defects occur more frequently in identical fetuses than in
fraternal ones. In rare cases, problems occur when the genetic material
(chromosomes) in the fertilized egg does not split evenly. This can result in
severe mental or physical defects in one or more fetuses.
Twins that are joined by any part of the body (conjoined) occur rarely. This occurs when the egg does not
split completely and the fetuses are partially joined.
Most doctors advise pregnant women to be screened for genetic disorders.