Most children conceived via assisted reproductive technology (ART), such as superovulation are fine, although some recent studies are raising doubts about whether these fertility fixes are as safe as promised. The extensive handling of these crucial cells is a concern, and there are mixed reports on the long-term health of these hard-won children, with several studies suggesting increased risks of low birth weight, rare disorders down the line, and even death.
For starters, one study published in July 2009 links ART embryos with poor health outcomes along a few dimensions. Another paper, from January 2010, shows that the genes in ART embryos bear different epigenetic marks than non-ART embryos. And the laboratory procedure of ART itself, during which eggs, sperm and embryos are typically sucked in and out of pipettes and left to sit in culture dishes, concerns some researchers and potential parents alike. Scientists such as Mellissa Mann, a researcher at Children's Health Research Institute in Canada and the University of Western Ontario, speculate that these manipulations could affect the health of ART babies.
"More attention should be paid to the safety of ART offspring as they now account for the large proportion of the population," says He-Feng Huang, an obstetrician and gynecologist at Affiliated Women's Hospital and Zhejiang University School of Medicine in China. Indeed, according to a 2009 study published in Human Reproduction, the number of ART procedures is on the rise and so-called test-tube babies account for an estimated 250,000 births every year worldwide.
ART encompasses several techniques: With superovulation, women receive high doses of hormones to stimulate egg production. Eggs and sperm are brought together in a dish so that in vitro fertilization (IVF) will take place. If a man's fertility is low a single sperm cell can be chosen and injected into an egg, forcing fertilization. Another procedure, called pre-implantation genetic diagnosis (PGD), involves removing one or two cells from an early-stage IVF embryo for genetic testing to screen for various diseases.
The 2009 health outcomes work, by biologists Ran Huo, Qi Zhou and colleagues at the Chinese Academy of Sciences and Nanjing Medical University, involved comparing mice that had undergone IVF and PGD with those that had undergone IVF alone. The team reported in Molecular and Cellular Proteomics that, compared with controls, PGD mice were more forgetful, heavier and had less myelin (a fatty coating on nerves that allows electrical signals to move quickly across nerve cells). They also expressed abnormal levels of proteins involved in neurodegenerative conditions.
Although mouse outcomes do not always parallel those in humans, the lab animal studies are helpful because "when we're studying humans, we can't separate out the effect of the procedure versus fertility issues," Mann says. For example, it is hard to say whether an ART baby has died because of the ART technology or because one of its parents had a mutation that mutually contributed to subpar fertility and infant death.
Mann's group, for the 2010 work on ART and epigenetics, used mice to examine changes on four genes following a superovulation procedure. The team looked at methylation, in which a methyl group is placed onto cytosine in DNA sequences. Methylation typically silences genes so that they are not expressed. Mann's team reported in Human Molecular Genetics that superovulation affected the establishment and possibly the maintenance of methylation in mice. Messed-up methylation early in development can cause disorders, such as Beckwith-Wiedemann syndrome (an overgrowth disorder), in humans. Another study by a different group in the same journal in October 2009 looked at ART effects on epigenetics (non-DNA changes in genes) in humans. They found methylation defects on several human genes in the cord blood and placentas of ART embryos, suggesting that a similar effect might be occurring in humans as well.
Cause and effect
Molecular studies paint a potentially bleak picture, but researchers warn that the effects and causes of these differences are unknown. "I think it's hard to make any firm conclusions so far," says Liv Bente Romundstad, a fertility doctor and researcher at Saint Olav's University Hospital in Norway.
To tease out the effects of ART from the impact of underlying fertility issues in humans, Romundstad's team studied mothers who had one pregnancy with ART and one naturally. Because the women had children on their own either before or after ART, the researchers assumed that fertility was not a problem. Multiple births were excluded because even naturally conceived multiples have a high risk of complications, Romundstad says.
When ART babies were compared with the entire population they had a lower birth weight and increased risk of death around the time of birth, but that risk disappeared when compared with their siblings. The analysis, published in August 2008 in The Lancet, suggests, "the infertility treatment per se for the outcomes we have studied does not seem to give any additional risk," Romundstad says.
But there's still reason for concern. In a talk at the European Society of Human Genetics conference this month, Géraldine Viot, a clinical geneticist at the Maternity Hospital, Port Royal in Paris described her team's large study of French ART centers. Although ART children had a slightly higher than normal rate of birth defects, their risk of developing epigenetic disorders, such as Beckwith-Wiedemann syndrome, was 4.5 to six times higher.
So, is ART safe? "For some of these children, we still don't know what the long-term results of the ART will be, in that a lot of these children are not yet reproductive age," Mann points out. Romundstad says that although it's possible that health effects could surface later on, she will continue to offer fertility treatment in her practice. "I don't think the timing is right to start to scare the population, but I think it's important to focus on this and continue with studies," she says.