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Multiple Pregnancy

Definition, Description, Causes and symptoms, Diagnosis, Treatment, Alternative treatment, Prognosis

Multiple pregnancy is a pregnancy where more than one fetus develops simultaneously in the womb.


Twins happen naturally about one in every 100 births. There are two types of twinning—identical and fraternal. Identical twins represent the splitting of a single fertilized zygote (union of two gametes or male/female sex cells that produce a developing fetus) into two separate individuals. They usually, but not always, have identical genes. When they do not separate completely, the result is Siamese (or conjoined) twins. Fraternal twins are three times as common as identical twins. They occur when two eggs are fertilized by separate sperm. Each has a different selection of its parents' genes. The natural incidence of multiple pregnancy has been upset by advances in fertility treatments, resulting in higher rates of multiple births in the United States. All these children are fraternal; they each arose from a separate egg and a separate sperm. Cloning produces identical twins.

The human female is designed to release one egg every menstrual cycle. A hormone called progesterone, released by the first egg to be produced, prevents any other egg from maturing during that cycle. When this control fails, fertilization of more than one egg is possible. Fertility drugs inhibit these controls, allowing multiple pregnancy to occur. Multiple pregnancy is more difficult and poses more health risks than single pregnancy. Premature birth is greater with each additional fetus.

The problem with multiple births is that there is only so much room in even the most accommodating womb (uterus). Babies need to reach a certain size and gestational age before they can survive outside the uterus. Prematurity is the constant threat of multiple pregnancies. Twins have five times the death rate of single births. Triplets and higher die even more often. The principle threat of prematurity is that the lungs are not fully developed. A disease called hyaline membrane disease afflicts premature infants. Their lungs do not stay open after their first breath because they lack a chemical called surfactant. Survival of premature infants was greatly improved when

An ultrasound image of identical twin male fetuses. The distortion is due to "twin B" being closer to the monitor. (Courtesy of Melissa Walsh Doig.) An ultrasound image of identical twin male fetuses. The distortion is due to "twin B" being closer to the monitor. (Courtesy of Melissa Walsh Doig.)

surfactant was finally synthesized in a form that could be of benefit to premature babies. Tiny babies also have trouble regulating their body temperature.

Causes and symptoms

Fertility drugs prevent the normal process of single ovulation by permitting more than one egg at a time to mature and ovulate (move from the ovary to the uterus in anticipation of fertilization). This happens naturally to produce fraternal twins. The first drug to accomplish this was clomiphene. Subsequently, two natural hormones—follicle stimulating hormone and chorionic gonadotrophin—were developed and used.


Multiple pregnancies cause the uterus to grow faster than usual. Obstetricians can detect this unusually rapid growth as the pregnancy progresses. Before birth, an ultrasound will also detect multiple babies in the uterus. After birth, physical appearance or a careful examination of the placenta and amniotic membranes will usually reveal whether the babies were in the same water bag or separate ones. One bag means identical twins.

A multiple pregnancy almost always means increased monitoring and surveillance for complications. This often means more frequent visits to the healthcare provider, serial ultrasounds to make sure that the babies are growing adequately, amniocentesis to check for lung development, and close monitoring for preterm labor.


Mothers may be put on bedrest during a multiple pregnancy, in order to try to prevent pre-term labor and delivery. If preterm labor is impossible to control at home, the mother may be hospitalized, and medication may be used to attempt to control contractions and dilatation of the cervix. Multiple pregnancies more often end in cesarean deliveries than singleton pregnancies.

Babies from multiple pregnancies are often born early, and may require longer-than-normal hospitalization. The babies may need assistance with breathing, careful control of body temperature within an incubator, and surveillance for other complications that frequently beset pre-term babies. While premature babies are fragile in many other ways, modern methods of intensive care have successfully stabilized babies as small as one pound.

Alternative treatment

There are no specific treatments to alleviate medical difficulties caused by multiple pregnancies, however there are supportive measures that may help both mother and children recover from the birthing process. There are treatments to encourage breast milk production and to combat postpartum difficulties. Various homeopathic remedies and massage can be helpful to both mother and children during the early adjustment period after birth.


With modern medical advances and excellent prenatal care, many multiple pregnancies reach fruition without difficulties. If the babies are born prematurely, immediate medical care increases the chance of survival without any complications.



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Cunningham, F. Gary, et al., eds. Williams Obstetrics. Stamford, CT: Appleton & Lange, 1997.


Evans, M.I., et al. "Selective Reduction For Multifetal Pregnancy. Early Opinions Revisited." Journal of Reproductive Medicine 42(December 1997): 771-777.

Evans, M.I., et al. "What Are The Ethical And Technical Problems Associated With Multifetal Pregnancy Reduction." Clinical Obstetrics and Gynecology 41(March 1998): 46-54.

Hecht, B.R., and M.W. Magoon. "Can The Epidemic Of Iatrogenic Multiples Be Conquered?" Clinical Obstetrics and Gynecology 41(March 1998): 126-137.

Kok, J.H., et al. "Outcome Of Very Preterm Small For Gestational Age Infants: The First Nine Years Of Life." British Journal of Obstetrics and Gynaecology 105(February 1998): 162-168.

Kousta, E., D.M. White, and S. Franks. "Modern Use Of Clomiphene Citrate In Induction Of Ovulation." Human Reproduction Update 3(July 1997): 359-365.

Styrcula, L. "Code Seven: The Birth Of The Septuplets." Nursing Spectrum 9(February 1998):14-15.

Rosalyn Carson-DeWitt, MD


Amniotic membranes—A thin membrane surrounding the fetus and containing serous fluid.

Genes—Hereditary determinants of identifying characteristics.

Gestational—Refers to pregnancy.

Ovulate—To release a mature egg for fertilization.

Zygote—The earliest stage of a fertilized egg.

Additional topics

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