Newly pregnant women often wonder: Could I be having more than one baby? The question is a reasonable one. In 2008, the twin rate was 32.6 twins out of every 1,000 newborns--a little more than 1 in 30 were twins. The birth rate for triplets and higher order multiples was 147.6 out of 100,000. While symptoms by themselves can't diagnose a multiple pregnancy, a number of symptoms do occur more frequently if you are carrying more than one baby.
The level of the pregnancy hormone human chorionic gonadotropin, or hcg, rises faster on average in multiple pregnancies than in singleton pregnancies. Betabase, a database listing hcg levels in thousands of successful pregnancies, shows that pregnancies with multiples consistently have higher average hcg levels than those of singles. From seventeen days past ovulation on, the median hcg level with twins is roughly double that of singletons, and triplet pregnancies have hcg levels close to three times that of singleton pregnancies. Similarly, a 1999 study in "Human Reproduction" by Sverre Bjercke, et al., found that 12 days after an embryo transfer, the average hcg levels for pregnancies with twins were approximately double that of pregnancies with one fetus.
Higher levels of pregnancy hormones can lead to earlier and more severe symptoms in a multiple pregnancy. According to Babycenter, women pregnant with twins can experience increased fatigue, constipation, nausea and shortness of breath. A 2006 study in "Obstetrics & Gynecology" by Deshayne B. Fell, et al., found that multiple pregnancies carried a higher risk of hypermesis gravidarium, a severe form of morning sickness that results in frequent vomiting, dehydration and excessive weight loss.
Measuring larger than expected based on gestational age can indicate multiples, since there are two or more fetuses expanding the uterus. Obstetrician-gynecologist Dr. Gerard M. DiLeo says that in the first and second trimesters, fundal height--the measurement of the uterus's size--can be one and a half to two times greater with twins than in a singleton pregnancy (see Resources section). As a result, you might find that your clothes become tight and you need to wear maternity clothes earlier than average.
Sometimes you might suspect multiples using a fetal doppler, a device that uses sound waves to detect a fetal heartbeat. However, using a doppler to diagnose twins is difficult because you might simply hear one baby's heartbeat twice, according to DiLeo. Background noise or the mother's heartbeat can also be confused with a second--or third--heartbeat. To increase the odds that you are hearing another fetus, the heartbeats should have different rates.
An ultrasound that at six weeks gestation shows more than one heartbeat is the most reliable method for diagnosing multiples before birth. However, Dr. Victor Klein, a perinatologist, points out that with higher-order multiples, even an ultrasound can miss one or more of them due to difficulties visualizing all fetses accurately (see Resources section).