Over the past 25 years, science has made great progress in helping women who are struggling to become pregnant actually conceive. Assisted reproductive technology or assisted conception, involves surgically removing the eggs from a woman’s ovaries, combining them with sperm in the laboratory, and then either returning the fertilized eggs to the original woman’s body or donating them to another woman. This process is commonly known as
fertilization or IVF
However, IVF is not without risk. For example, women who become pregnant through IVF have a much greater chance of multiple births (twins or more) than women who become pregnant naturally. But, does this tendency increase the risk of a poor health outcome for children born to women who used IVF? A study published in the January 23, 2004 issue of the
British Medical Journal
looked at natural and IVF conceptions to determine if there were differences in pregnancy outcomes.
About the study
The researchers conducted a systematic review of the medical literature and identified 25 studies comparing women who gave birth to either one child or twins. Of these, 17 studies used matched controls, meaning that every woman who became pregnant using IVF was compared to a woman with similar characteristics who became pregnant naturally.
The researchers compared the relative risk of a poor health outcome for babies born both naturally and through IVF. These poor health outcomes were defined as:
Low birth weight
Small size at birth
Need for a caesarean section
Admission to the neonatal intensive care unit of a hospital
Relative risk is a measure of the association between an exposure and a health outcome. In this case, the exposure is IVF conception and the health outcome is poor health at birth. A relative risk of 1.0 would mean that a baby conceived through IVF had
no greater or lesser risk
of a poor outcome than a baby conceived naturally. A relative risk of 2.0 would indicate that a baby conceived with IVF had
twice the risk
of a poor outcome as compared to a baby conceived naturally. A relative risk of less than one would indicate that IVF conception had a protective effect. For instance, a relative risk of 0.80 would mean that IVF conception reduced the baby’s risk of a poor outcome by 20%.
The researchers found that IVF conception increased a single baby's risk for a poor health outcome, in some cases significantly. Single babies conceived through IVF were three times more likely to be very preterm and twice as likely to be preterm than single babies born to mothers who conceived naturally. They were also three times more likely to have a very low birth weight and almost twice as likely to have a low birthweight. The following table lists the relative risks for babies conceived through IVF in all health outcomes measured for both single births and twins.
Relative Risk for IVF Conception as Compared to Natural Conception
Poor Health Outcome
Very preterm (<32 weeks)
Preterm (<37 weeks)
Very low birth weight (<1500 grams or <3.3 pounds)
Low birth weight (<2500 grams or < 5.5 pounds)
Small for gestational age
Neonatal intensive care unit
Perinatal mortality (stillbirth and death within first week)
*Results are from matched studies; non-matched studies showed similar results.
As illustrated in the table, the findings were not similar for twins conceived through IVF. In fact, one surprising result was that IVF conception appeared to have a protective effect in several outcomes for twins. For example, in twin pregnancies with IVF, the relative risk of perinatal mortality was about 40% lower than with natural conception.
How does this affect you?
The authors of the study concluded that doctors should inform all women undergoing IVF of the increased risk in single pregnancies. In addition, they strongly suggest that the focus of IVF be shifted from simply achieving pregnancy to achieving the birth of healthy children.
If you are having problems conceiving, should these findings keep you from trying IVF? Absolutely not; IVF has had many successes. But before making a decision, keep in mind that the ultimate reason for IVF is not to become pregnant, it’s to become a parent of a healthy baby. Setting your sights on this goal will allow you to make a more realistic decision among all the options at your disposal, including adoption.
CDC’s Reproductive Health Information Source. 2001 Assisted Reproductive Technology Success Rates: National Summary and Fertility Clinic Reports. Centers for Disease Control and Prevention Web site. Available at:
. Accessed January 28, 2004.
Helmerhorst FM, Perquin DAM, Donker D, Keirse MJNC. Perinatal outcomes of singletons and twins after assisted conception: a systematic review of controlled studies.
Hennekens CH, Buring JE.
Epidemiology in Medicine
. Boston, Ma: Little, Brown, and Company, 1987.
Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a