
I write this post after being told I would need a scheduled caesarean when a low-lying placenta (LLP) was found at my 20-week morphology scan. As a birth doula, and having supported women who had a similar experience, I didn't think for a second about the ultrasonographers' certainty of a scheduled caesarean. My partner, unfortunately, didn't have the knowledge I did at the time and after the scan, told me he completely checked out after this comment and became so concerned for me and the baby.
This prompted me to think about all the couples told this during their 20-week scan and don't have the information about a low-lying placenta, and how it can impact their experience.
My placenta was 0.4mm away from my cervix at this point... so, quite close. As I naturally do, I searched the databases I have access to for low-lying placenta studies and evidence. I also listened to a few reputable podcast episodes on low-lying placentas and wanted to share this information with others who may find themselves in the same boat. Though I wasn't all that concerned, just reading all of this information I felt 100% a-okay about my chances of the placenta being far enough away from my cervix.
At 34 weeks, my placenta was 3.4mm away from my cervix.
A low-lying placenta is one that is less than 20mm away from the cervix. Having a placenta close to the cervix can increase your risk of certain outcomes, but does not guarantee it as a placenta previa might (where the placenta is covering part or all of the cervix). It is important to consider how much the uterus grows from 20 to 40 weeks, and how that growth impacts the position of the placenta in relation to the cervix.
The third trimester contributes to your baby putting on 70% of their weight, so you can imagine how drastic the growth of your uterus is at this time. As the uterus grows, so does the how close the placenta is to the cervix (if it is low lying).

If you have a balloon at home, this is a great exercise to see how the space between the placenta and cervix likely will move over time. The dot on this image is the placenta, the white line is the cervix. As you blow the balloon up (aka, the uterus growing to its full size), you will see this dot (aka the placenta) move further and further away from the white line (aka the cervix).
Podcasts I recommend you listen to
If you have been told you have a low lying placenta and you are worried for what it means for your birth, listen to these podcast episodes (click on the name and it'll redirect you):
The Great Birth Rebellion - Low Lying Placentas
The Homebirth Midwife Podcast - Low Lying Placentas and Homebirth
Studies and evidence on low lying placentas
A US study of 503 pregnancies that were diagnosed a LLP between 18-24 weeks = all except 2 were resolved by 34 weeks (further than 2cm away from the cervix). Which means based on this study, you have a 99.6% of LLP resolution by 34 weeks. They did find an increased risk of admission for antepartum bleeding for those who had a cervix to placenta distance of below 0.5cm.
A NZ based study looked at 350 women diagnosed with a LLP at the 18-20 week scan and found 317 (91%) had a placenta clear of the 2cm distance on their follow up scan whilst the remaining 9% had a persistent placenta praevia
A India based study found a LLP was found to migrate to upper uterine segment in 77.3% of cases. The rate of migration was decreased in cases where placenta was closer to the cervix and those that were overlapping the cervix.
A 2019 systematic review and meta-analysis found that a vaginal delivery was successful 43% for a cervix to placenta distance of 0-10mm, 85% for 11-20mm distance and 82% of a distance greater than 20mm (not considering other reasons for an unsuccessful vaginal delivery)
American Journal of Obstetrics and Gynecology found no significant correlation between the distance of the cervix and placenta at 20 weeks and how long it took for this to resolve (to move beyond 2cm). They also found a 99.14% resolution rate for women with low-lying placentas
American Journal of Obstetrics and Gyneocology found no significant correlation between trial of labour and severe postpartum haemorrhage in women with with a low lying placenta that gave birth after 35 weeks gestation
a 2014 study found that in 1240 pregnancies observed, 1220 (98.4%) resolved to no previa before delivery. 89.9% cleared by 32 weeks, and 95.9% cleared by 36 weeks. 20 patients (1.6%) had persistent placenta previa or a low lying placenta at or near term
A 2018 study of 1663 women with a LLP or placenta previa found a median time for resolution was 10 weeks (7-13 weeks). They also found those with a LLP between 10-20mm had a 99.5% resolution rate, those with 0.1-10mm had a 95.4% resolution rate and those with placenta previa had a 72.3% resolution rate.
This is just a small handful of studies I found, but there are plenty more to read. Always trust your own intuition regarding your unique circumstances, chat with your trusted care provider and do your own research.
I would recommend, based on the research, if you're wanting a follow up ultrasound to check your placenta location, to do so after 10 weeks from your previous ultrasound (based on the above research).
You are the expert of your body.
References:
A Cross Sectional Study of Second Trimester Sonographically
Diagnosed Low-Lying Placenta and Associated Maternal and Neonatal Outcomes at Delivery
Low-lying placenta: Who should be recalled for a follow-up scan?
Outcome of low-Lying placenta at 18-22 Weeks- A Prospective Observational Study
Vaginal delivery in women with a low-lying placenta: a systematic review and meta-analysis
Outcomes of Pregnancies With a Low-Lying Placenta Diagnosed on Second-Trimester Sonography
Resolution of a Low-Lying Placenta and Placenta Previa Diagnosed at the Midtrimester Anatomy Scan
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