Fertility Blog

ART and Birth Outcomes

Assisted reproductive technology (ART) has been a part of modern medicine now for over 30 years and in the US alone over 132,000 IVF cycles were performed in 2007. All birth outcomes are reported to the Centers for Diseases Control but there is no mechanism for long-term follow-up of IVF births.

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Well over a million babies have been born world wide through IVF and new data are emerging about reproductive birth outcomes after conception. Some countries, particularly the Scandinavian countries, do an excellent job on gathering data for all births, including IVF-conceived births. One of the greatest risks of ART is prematurity from multiple gestation. From several of these databases, it has become apparent that even singleton IVF births are statistically associated with poorer birth outcomes. Lower birth weights, pre-term delivery and infants small for gestational age (i.e. lower weight than expected for number of weeks in utero) are some of the findings from follow up of IVF babies. These findings beg the question: is it something about IVF, namely the culture of the early embryo in a lab for the first three to five days of life, that results in these poorer outcomes, or is it something about the couples that need IVF to conceive that is associated with them? This can be a difficult issue to sort out because relatively few people undergo IVF who are not infertile. A recent study from Norway was published in the British medical journal Lancet that tried to address this question by comparing IVF babies with their spontaneously-conceived siblings. The study compared 1,200,922 spontaneously-conceived live births and compared them with 8,229 live births after ART between January 1984 and June 2006. Of those women who had given birth to a singleton infant after ART, 2,456 also delivered a singleton infant after spontaneous conception. In 56% of the cases, the ART baby was born first and in 44% the ART baby was conceived after the birth of the spontaneously-conceived infant. The researchers looked at birth weight, gestational age as well as a number of other factors. Compared with women in the general population that delivered a spontaneously-conceived birth, the women that delivered after IVF were older, less likely to smoke and had fewer previous births. Induced labor and cesarean section were more common in the IVF moms. The difference in birth weight between ART and non-ART babies was 131 grams (4.6 ounces). That is, the ART babies weighed, on average, 4.6 ounces, or about 3/4 pound less than the spontaneously-conceived babies. After statistical adjustment for gestational age, maternal age, prior births, year of birth, the difference in birth weight between ART and non-ART babies was 25 grams (0.88 ounces). The ART babies were born, on average, 3.7 days earlier than the controls. After statistical adjustment, the number of days of total gestation was 2 fewer days. Because of the large sample size, these were statistically significant differences but realistically, they were probably not clinically significant. In comparing the sibling relationship ART vs. non-ART births, the differences were even smaller. The difference in birth weight was only 87 grams (about 3 ounces) for the ART babies as compared to their spontaneously-conceived siblings. The gestational age differences at birth were 1.3 days less for ART. After adjustment, these differences were only 9 grams and 0.6 days. These differences were not even statistically significant. From these data, we can see that ART births do show statistical differences in some birth outcomes as compared to spontaneously conceived births. However, none of the differences seem are to an extent that would have any real clinical meaning. These differences tend to disappear to a large extent when comparing siblings from both spontaneous and IVF conception, suggesting that it is something about the families that utilize ART, rather than the technique itself that may be associated with the outcome differences.
Posted on July 22nd, 2009

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