What is the chance of miscarriage after seeing heartbeat on ultrasound? I’ve found myself googling that exact question several times over the past 2 years as I dealt with my fears and anxiety after recurrent miscarriages. Statistics can’t tell us what our personal experience will be, but they can give us more hope and confidence. Cohort studies have been able to shed some light on the chances of successful pregnancy after a viable early ultrasound.
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What is an early ultrasound?
An early ultrasound, also called a dating scan, is the first ultrasound of a pregnancy that usually occurs in the first trimester. This can be as early as 6 weeks with a transvaginal ultrasound, but many providers prefer an early ultrasound between 8-12 weeks.
In an early ultrasound, the provider should be able to see the baby and find the baby’s heartbeat. At this stage, you won’t be able to listen to the heartbeat, but they can see it on the screen. The provider can also measure the size of the baby. This is also the most accurate time to confirm the baby’s gestational age and your due date. While growth is measured at ultrasounds after 12 weeks, these later ultrasounds are less accurate for estimating due date.
What is a good early ultrasound?
There are two things that help tell us about the health of the baby, the embryonic heart rate and the ratio of gestational sac to crown-rump length.
Embryonic heart rate
The embyronic heart rate is simply the heart rate of the baby. The baby’s heart rate can be measured from around 6 weeks, but if you are going in for an ultrasound at 6 weeks, be prepared for the possibility that your provider may not be able to find a heartbeat yet.
Gestational age of the baby can vary depending on date of ovulation and the amount of days for implantation to occur. This means that the baby’s gestational age may be more or less than your expected due date, even if you were tracking closely. If ovulation was late, or implantation took longer than average, your baby might be a few days smaller than you think. This isn’t bad; it just means that your baby is 5 weeks gestation and you might not see a heartbeat yet.
The expected heart rate of the baby changes somewhat depending on the gestational age, but it is higher than what you would expect for you and I as adults. The normal embryonic heart rate is between 115 to 160 beats per minute. A heart rate that is low could be a sign of trouble, but not necessarily, especially if the ultrasound is early. Always listen to your provider’s opinion before panicking!
Ratio of gestational sac volume to crown-rump length
The gestational sac is the first part of the pregnancy that can be seen on ultrasound. It is a fluid-filled area where the baby begins to grow, first as a yolk sac that will become an embryo. By 6 weeks, a very small fetal pole can be seen in the yolk sac – that fetal pole is your baby, even though it’s only 1-2mm big! From 6 weeks to 10 weeks, the fetal pole grows about 1mm per day. The size of the fetal pole (your baby) is called the crown-rump length. This is because baby’s in early development are often curled up, even though in the early first trimester, you can’t actually tell the head from the rump.
The ratio of gestational sac volume to crown-rump length can help tell your provider if your baby is growing well. If both the gestational sac volume and the crown-rump length are smaller, the baby may be behind your predicted dates. If both the gestational sac volume and the crown-rump length are larger, the baby may be a few days older than you anticipated. However, if the gestation sac is of a certain size, and but the growth of the yolk sac or fetal pole is behind, that is a cause for concern. Your provider may order repeat ultrasounds if they have a concern about growth.
What is the chance of miscarriage after seeing heartbeat by week?
So you had a good ultrasound, the baby is in there and the heart is beating. Now what are the chances you will go on to have a successful pregnancy? Based on a cohort study by Tong et al, the risk of miscarriage after a visit between 6-11 weeks gestation with a viable fetus (baby with a heartbeat) is 1.6% or less. Those who had a good ultrasound at 6 weeks had the highest chance of miscarriage, but the risk dropped dramatically for women who had a good ultrasound at 8 weeks gestation or later. Here’s the breakdown:
- 6 weeks – 9.4% risk of miscarriage
- 7 weeks – 4.2% risk of miscarriage
- 8 weeks – 1.5% risk of miscarriage
- 9 weeks – 0.5% risk of miscarriage
- 10 weeks – 0.7% risk of miscarriage
Considerations when scheduling an early ultrasound
I want to encourage you to follow the advice of you provider, whatever that may be. They may have specific reasons for requesting you have an early ultrasound at a certain time.
But, if your provider gives you options, when is the best gestational age to schedule? There are benefits to scheduling early, and to waiting a week or two. For those of us who have ended up on the wrong side of statistics before, scheduling early may bring relief. You may be able to see a heartbeat and feel some sense of comfort. However, if you want to wait until you can be more sure of the result, 8 weeks seems to be the sweet spot of increased confidence with the least waiting. If you can wait until 8-9 weeks gestation, and you see a heartbeat on ultrasound, you can have confidence that your miscarriage risk is now very low.
Citations:
- Tong S, Kaur A, Walker SP, Bryant V, Onwude JL, Permezel M. Miscarriage risk for asymptomatic women after a normal first-trimester prenatal visit. Obstet Gynecol. 2008 Mar;111(3):710-4. doi: 10.1097/AOG.0b013e318163747c. PMID: 18310375.
- https://obgyn.onlinelibrary.wiley.com/doi/full/10.1111/ajo.12395
- https://ultrasoundpaedia.com/foetal-heart-normal/
- Dewald O, Hoffman JT. Gestational Sac Evaluation. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551624/