A new study questions the validity of guidelines for detecting first trimester pregnancy losses and could mean waiting two weeks instead for one for your diagnosis.
When pregnant women go for their first ultrasound, it is usually a time of joy. But for some, an early ultrasound can lead to uncertainty about their pregnancy and requires a followup. Waiting to find out if you're going to have a miscarriage can be brutal, but it's crucial that doctors get it right so they don't misdiagnose a pregnancy that's actually viable—a rare occurrence, but something that shouldn't happen at all. A new study published this week in the British Medical Journal is advising that the waiting period in between ultrasounds be even longer—two weeks instead of one—to make sure not even one pregnancy is misdiagnosed as a miscarriage.
Avoiding a misdiagnosis
The observational study looked at over 2,800 women in London who had early pregnancy scans because of pain, bleeding, severe morning sickness or a history of miscarriage or ectopic pregnancy, and whose ultrasounds suggested their pregnancies might not continue. The women were asked to return for a repeat scan in seven to 14 days, and the researchers followed up to see what the final status of the pregnancy was at 11-14 weeks. "Having this data we were able to look at how well current guidelines used to diagnose miscarriage [in both the U.S. and the U.K.] perform, and to make proposals that might improve things," study author Tom Bourne, M.D., Ph.D., an OBGYN and professor at Imperial College London, tells Fit Pregnancy. "The key issue being that there cannot be any error based on guidelines that may be associated with a false positive diagnosis for miscarriage, i.e. saying the pregnancy has miscarried when it hasn't."
The researchers looked at the data against the current standards for when the embryo should be present in the gestational sac, how big the embryo should be and when a heartbeat should be seen. They found that the criteria used to diagnose miscarriage on second ultrasounds, which normally occur after one week, were not always accurate—in the study, up to 19 out of 578 (3.3 percent) of cases would have been misdiagnosed. However, the study showed that if the second ultrasound was two weeks after the first instead of one, the diagnosis of miscarriage was always correct. "Even one misdiagnosis is very important," Bourne says. "The main recommendation is that when an initial scan is uncertain, the time before a scan is repeated to decide if there is a miscarriage or not is extended to 14 days."
Experts here in the States agree that stricter standards for avoiding a misdiagnosis of miscarriage should be put into practice, if they aren't already. "These guidelines provide ultrasound criteria that make this even less likely to happen than with past criteria that already made it very unlikely," Jeffrey Ecker, M.D., a high-risk OB at Massachusetts General Hospital and the chair of the American Congress of Obstetricians and Gynecologists' Committee on Obstetric Practice, tells Fit Pregnancy. "They should certainly guide practice here in the United States and, in fact, are likely already in place at many centers."
When an ultrasound isn't clear
Uncertain ultrasounds often occur in possible cases of a "blighted ovum," in which a gestational sac doesn't appear to have developed a baby inside it. In this situation, a pregnant woman might not even be aware that something is wrong. "The ones where an error is most likely is when on an initial scan there is an empty gestational sac and the mean sac diameter is less than 12 millimeters," Bourne says. "In these circumstances it is important to wait longer, at least 14 days, before repeating a scan to make a definitive diagnosis of whether there is a miscarriage or not." If the embryo has not developed further at that point, it's clear that the pregnancy has been lost.
A questionable scan also could occur in the case of an ectopic pregnancy, where the embryo implants somewhere else besides the uterus—a potentially life-threatening situation in which early detection is crucial. "The first and most critical question in evaluating an early pregnancy is to determine whether it is in the uterus or outside of the uterus, i.e. an ectopic pregnancy," Zev Williams, M.D., Ph.D., director of the Program for Early and Recurrent Pregnancy Loss at Montefiore Health System in the Bronx, N.Y., tells Fit Pregnancy. "Once a pregnancy has been confirmed to be in the uterus, there is no longer any medical necessity to rush a definitive diagnosis and even take a small chance of being wrong."
Another difficulty in diagnosing a miscarriage could happen if a woman is uncertain about her last period, which would affect the dating of the pregnancy and how big the embryo should be. "In the case of early pregnancies, the embryo can look much smaller and less developed than expected if the woman ovulated later than she thought and the pregnancy is therefore younger than expected," Williams says.
But, doctors also use other information besides ultrasound in making a diagnosis. "It is important to note that ultrasound is often not the only tool used to diagnose an early pregnancy failure, and clinicians will often incorporate other information—for example timing and values of past blood or urine pregnancy tests—to evaluate how far along a pregnancy should be and/or its underlying health," Ecker says. In his experience, Williams says, "waiting one week is usually more than sufficient. I don't think a two-week delay is necessary."
Whether to "wait and see"
Bourne admits there are downsides to waiting longer before making a diagnosis of miscarriage. "Waiting to know if a pregnancy is viable or not can be distressing," he says. There are practical concerns as well. "In order to determine the cause of the miscarriage it is often critical to send a sample of the placenta for genetic testing, and this may not be possible if the pregnancy remained inside the woman for too long after it demised," Williams says. But, "when genetic testing does not need to be done, the woman can safely opt to allow the pregnancy to pass on its own and can be given several weeks for this to happen."
The decision to allow a miscarriage to happen naturally, which can involve pain and bleeding, or to have a surgical procedure to remove it, is very personal. Waiting longer to confirm the miscarriage may mean that the process starts to happen on its own. "For some women allowing a natural process of miscarriage to occur would be their choice, however others may have chosen surgery or medical management," Bourne says. If you're faced with a possible miscarriage, talk through all the options with your doctor. "Should a woman not wish to wait two weeks before having a repeat scan to determine if a pregnancy has miscarried, then she should raise her concerns with her doctor and have an informed discussion about the risks of misdiagnosis for her specific pregnancy in order to make an informed decision. Any women should feel able to discuss any aspect of her care with her doctor."