“What are the chances?” we ask with some frequency around the FiveThirtyEight offices. But when it comes from a colleague who’s trying to make sense of getting pregnant within just a couple of weeks of her wife, it commands some out-of-the-ordinary attention. Two pregnant women, due three weeks apart. “When we found out, we were super excited,” said Kate Elazegui, FiveThirtyEight’s creative director. “But when we walked out of the doctor’s office, we were like, ‘Holy shit.’”
Kate agreed to let me explore her question and gave me the details of how she and her wife went about getting pregnant. There are a lot of statistics available on assisted reproductive technology, so I thought finding an answer would be fairly straightforward. But it turns out that, as these things often go, getting to the bottom of her “what are the chances?” question was a lot more complicated than I’d thought.
Kate and her wife, Emily, knew they wanted children, probably two. This would require a sperm donor, so they went to a fertility clinic, searched through hundreds of donor options, and bought out the stock from their first choice. Emily and Kate were both interested in carrying a baby with their own eggs.1 If all went as planned, one of them would get pregnant, and a couple of years later, the other would use the remaining sperm to have a second child. The doctor suggested that Emily go first, since she’s a few years younger and therefore statistically more likely to be successful. But for that same reason, the couple had decided that Kate would give it the first go. At 40, she still had a reasonable chance of getting pregnant, but that chance would diminish quickly over the next couple of years.
Kate started with intrauterine insemination, IUI, a treatment that involves inserting sperm into a woman’s uterus. Five months in, she wasn’t pregnant, so she moved on to in vitro fertilization, IVF, which offers a higher chance of pregnancy but is much more expensive and physically demanding. For the procedure, an egg is manually combined with sperm in a lab, and the fertilized egg is then transferred to the uterus.
As Kate neared the end of a first round of treatment, the couple’s doctor suggested that Emily get started. For women age 37, 28.2 percent of IVF treatments end in pregnancy, compared with 18.7 percent of treatments for women age 38 to 40. By 41, success drops to 10.7 percent per treatment cycle, according to the Society for Assisted Reproductive Technology (SART). Kate’s and Emily’s treatments would overlap by a few weeks, but the couple’s doctor wanted to maximize the potential that one of the women would have a successful pregnancy, and statistically, it was unlikely that Emily would get pregnant on the first try. Kate remembers asking whether they could both end up pregnant: “The doctor just kept saying, ‘It’s not going to happen, Kate. The odds are slim.’ And I kept saying, ‘Slim isn’t a number.’”
And so, as Kate neared the end of her first cycle of IVF, Emily did her first IUI treatment, using no hormones or injections. The couple saw it as early preparation for the “real” treatments, those that would involve drugs to improve the chance of a pregnancy. But within two weeks, they had good news: Emily was pregnant. They could have stopped Kate’s treatment, but she was so close to the end of the many expensive weeks of an IVF cycle, and the likelihood of Emily losing her pregnancy was high enough, that they decided she should finish. That was six months ago. Today the two sport matching baby bumps. “It’s the literal representation of brother from another mother,” Kate said.
The field of assisted reproductive technology — we’re talking mostly IVF here — is pretty rich in statistics. But while trying to calculate the likelihood of Kate and Emily both getting pregnant, I realized some key information was missing. The statistics don’t account for same-sex couples and single women, who generally seek treatment for different reasons than heterosexual couples.
Heterosexual couples mostly seek medical assistance because they have fertility issues (which affect about 12 percent of women, regardless of marital status or sexual orientation), while gay couples and single women often just need assistance.
The Centers for Disease Control and Prevention (CDC) gathers the IVF success rates for nearly all fertility clinics in the United States. But the data is reported by cycle of treatment, not patient, so it can’t be used to calculate a cumulative likelihood of success for an individual woman. SART also gathers data from member clinics, and has an online calculator for likelihood of a successful treatment that takes into account diagnosis and can calculate cumulative attempts.
According to SART, the probability of having a baby after one IVF cycle is 17 percent for a 40-year-old woman like Kate.2 Data on success rates with insemination is more complicated — the CDC and SART don’t keep comprehensive data on IUI, and many women insert the sperm at home or in a nonspecialty clinic, meaning successful pregnancies aren’t necessarily reported. Best estimates from the American Society for Reproductive Medicine (ASRM) say the IUI success rate can be as high as 20 percent, but that doesn’t capture variations by age and fertility status. An oft-cited study puts the success rate for a woman in her late 30s closer to 10 percent on the first IUI attempt, and at about 40 percent after five attempts.3
So say we go with those numbers: five failed IUI attempts and a successful first IVF cycle for Kate, and an initial successful IUI attempt for Emily. Voila, the probability of them both getting pregnant at the same time was about 1 in 100.
The actual probability, however, may have been much higher — we can’t be sure because we lack the data to evaluate success rates for people without fertility problems. Dr. Owen Davis, associate director for IVF at Weill Cornell Medical College and president-elect of ASRM, said that lumping in single women and gay couples with heterosexual couples probably skews the data, making success rates for heterosexual couples seem better than they really are because the numbers include outcomes for people with no known fertility problems. That means the statistics may underestimate the likelihood of a pregnancy for a same-sex couple. Davis said he’s seen an increase in same-sex couples and single women at his clinic in recent years, and he believes they have an easier time getting pregnant, because they’ve come to the clinic for fertilization, not necessarily because of individual fertility limitations. But he’s quick to note that his observation isn’t a scientific finding: His clinic is in the middle of New York City, so he can’t say whether the increase in numbers and the better outcomes are occurring in other parts of the country.
Sheree Boulet, a health scientist in the CDC’s Division of Reproductive Health, said a change in the surveillance protocol was recently approved that will allow for identification of same-sex couples and single women without fertility issues, but that information won’t be available until at least 2017.
Only a few studies exist on success rates for same-sex couples, and they are of poor quality at best. In a review of those studies, Juan Tarín, a professor at the Universitat de Valéncia in Spain, found that lesbian couples tend to have higher success rates than heterosexual couples who seek IVF and IUI treatment. The data isn’t exclusive to the U.S., making it hard to compare with the CDC or SART data, and also doesn’t account for age, one of the most important predictors. Still, it does suggest that success rates for same-sex couples could be higher than the U.S. data would imply.
Understanding the limitations of the statistics will be important for people preparing to spend tens of thousands of dollars on treatment. Same-sex couples and single women attempting IVF often have to pay more than heterosexual couples because their insurance is less likely to cover the treatment. State mandates on what kinds of fertility treatments insurance companies must cover, and for whom, vary widely. But rarely do they cover IVF for gay couples without known fertility issues. Experts on lesbian, gay, bisexual and transgender health say this is discrimination based on sexual orientation and will have to change to catch up with the law.
Meanwhile, Kate and Emily have gotten over the initial shock of what Emily calls “winning the baby lottery” and are enjoying the shared experience of being pregnant. “When you’re in a straight couple, your husband isn’t going to be able to feel what you’re feeling. With us, Emily is a couple weeks ahead of me, so we can compare notes,” Kate said. “As partners go, it’s been a good thing so far.” Except when one of them drops something. “Then we just look at each other.”
CORRECTION (Sept. 18, 7:50 a.m.): An earlier version of this article incorrectly stated the length of time between the two women’s due dates. It is three weeks, not two.