Overview of Multiple Pregnancy
What is multiple pregnancy?
Multiple pregnancy is a pregnancy with two or more fetuses. Names
for these include the following:
- Twins - 2 fetuses
- Triplets - 3 fetuses
- Quadruplets - 4 fetuses
- Quintuplets - 5 fetuses
- Sextuplets - 6 fetuses
- Septuplets - 7 fetuses
While multiples account for only a small percentage of all births
(about 3 percent), the multiple birth rate is rising. According
to the National Center for Health Statistics, the twin birth rate
has risen 59 percent since 1980, and is currently 31.1 per 1,000
live births. The birth rate for triplets and other higher order
multiples has also risen a staggering 423 percent. However, since
1998, the birth rate for triplets and higher has slowed.
What causes multiple pregnancy?
There are many factors related to having a multiple pregnancy.
Naturally occurring factors include the following:
- heredity
A family history of multiple pregnancy increases the chances
of having twins.
- older age
Women over 30 have a greater chance of multiple conception.
Many women today are delaying childbearing until later in life,
and may have twins as a result.
- high parity
Having one or more previous pregnancies, especially a multiple
pregnancy, increases the chances of having multiples.
- race
African-American women are more likely to have twins than any
other race. Asian and Native Americans have the lowest twinning
rates. Caucasian women, especially those over age 35, have the
highest rate of higher-order multiple births (triplets or more).
Other factors that have greatly increased the multiple birth
rate in recent years include reproductive technologies, including
the following:
- ovulation - stimulating medications such as clomiphene
citrate and follicle stimulating hormone (FSH) help produce
many eggs, which, if fertilized, can result in multiple babies.
- assisted reproductive technologies - in vitro fertilization
(IVF) and other techniques may help couples conceive. These
technologies often use ovulation-stimulating medications to
produce multiple eggs which are then fertilized and returned
to the uterus to develop.
How does multiple pregnancy occur?
Multiple pregnancy usually occurs when more than one egg is fertilized
and implants in the uterus. This is called fraternal twinning
and can produce boys, girls, or a combination of both. Fraternal
multiples are simply siblings conceived at the same time. However,
just as siblings often look alike, fraternal multiples may look
very similar. Fraternal multiples each have a separate placenta
and amniotic sac.
Sometimes, one egg is fertilized and then divides into two or
more embryos. This is called identical twinning and produces all
boys, or all girls. Identical multiples are genetically identical,
and usually look so much alike that even parents have a hard time
telling them apart. However, these children have different personalities
and are distinct individuals. Identical multiples may have individual
placentas and amniotic sacs, but most share a placenta with separate
sacs. Rarely, identical twins share one placenta and a single
amniotic sac.
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