After conception, your baby’s placenta implants in your uterus, in no specific position.
It might implant in a low, high, posterior (back), or anterior (front) position.
Usually, at the 20-week pregnancy ultrasound, you’ll start hearing about your placenta’s position.
If you have a low-lying placenta, you might wonder what that means for your pregnancy and birth.
Read on for more information.
Low lying placenta
The placenta is an organ that grows in pregnancy and is responsible for supporting your baby’s growth. It transports vital oxygen and nutrients to your baby and removes waste products.
A low placenta means the placenta has implanted in the lower part of the uterus. Sometimes it is close to the opening of your cervix (internal os).
How is low lying placenta diagnosed?
It’s recommended all pregnant women have a detailed pregnancy ultrasound at 20-22 weeks. By this time your baby is developed enough so that any abnormalities can be screened for.
At the same time, the scan checks your uterus, cervix, and the position of the placenta. If this organ is low in the uterus, you will be referred to have another scan at about 32 weeks.
The follow-up scan will check whether the placenta:
- Has moved up as the uterus has stretched
- Has stayed where it was (persistent low placenta)
- Is very close to, or covering the cervix (placenta previa)
What is the difference between a low-lying placenta and placenta previa?
If the placenta is close to the edge of the cervix it’s called low lying. When it is partially or completely covering the cervix, however, it’s a condition known as placenta previa.
How common is a low lying placenta at 20 weeks?
It’s estimated 1 in 20 women will be told their placenta is low at their 20-week ultrasound scan.
The evidence shows most placentas move as the womb grows; this is positive news for mothers with this diagnosis.
Don’t worry. There’s a very high chance that a low placenta will no longer be a problem by the time you have your third-trimester scan.
“My placenta was low lying (15mm or 1.5cms) at 20 weeks. A repeat scan at 27 weeks showed that it had moved to 40mm (4cms) and, at birth, it became a retained placenta (wouldn’t come out). I had to have it manually removed under a general anesthetic. It had moved all the way up and became stuck at the top of my uterus!” — Amy, BB Fan
How often does low lying placenta correct itself?
In this report by the Journal of Ultrasound Medicine, 89.9% of placentas moved by the 32-week ultrasound scan and 95.9% cleared by 36 weeks.
The National Health Service (NHS) report shows that 1 in 200 women will continue to have a diagnosis of placenta previa.
Posterior low lying placenta
If your placenta positions itself towards the back of the uterus, it’s called a posterior placenta.
A low posterior placenta means it’s lower to the cervix at the back of the uterus, and will most likely move away.
Anterior low lying placenta
An anterior placenta implants itself in the front section of the uterus. It can also be low and in most cases will move out of the way of the internal os as the womb grows.
It really makes no difference whether the placenta implants low either anteriorly or posteriorly.
What causes low lying placenta?
Certain factors influence where the placenta will implant in your womb and increase your risk of developing placenta previa.
These risk factors include:
- Fertility treatment. This can often play a part, due to the influence of where the embryo is implanted; the lower it’s implanted the higher the success rate.
- Uterine fibroid removal. This, and other previous abdominal surgeries, such as a c-section, can leave scar tissue that can influence where the placenta implant.
- Baby’s position. Sometimes babies are tricky and put themselves in strange positions, such as breech or transverse (lying sideways). This can cause the placenta to be low and not move up.
- Twin pregnancy.
- Pregnancy over 35 years of age.
- Smoking or using illicit drugs – before or during pregnancy.
- Abnormally shaped womb.
- Previous pregnancies.
Is it bad to have a low lying placenta?
It’s not necessarily a bad thing for your placenta to be low. It just means you’ll need to have more checkups as your pregnancy progresses.
The lower part of your uterus does most of its growing and stretching in the third trimester of pregnancy, until around 36 weeks. During its growth, it will usually take the placenta with it.
The placenta doesn’t actually migrate upwards because it’s attached to the uterine wall. Instead, it’s carried upwards with the uterus and pregnancy growth.
Low lying placenta precautions
Restrictions such as bed rest, no sex, and no lifting are usually prescribed only for women who have placenta previa (where the placenta is covering the internal os). Sometimes this applies to those who risk complications and blood loss due to a low placenta close to the edge of the cervix.
You should contact your doctor immediately if you have a low placenta and experience:
- Vaginal bleeding, including spotting
- Pain, including any mild period-like aches
How close to the cervix can my placenta be?
Some doctors will be happy if the placenta is 2cms (20mm) from the os (cervix). Other doctors prefer it to be 3cms (30mm) from the opening.
Given the variation in measurements, if you want to have a vaginal birth, you should definitely be given the opportunity.
The exceptions are when the internal os is covered by the placenta, and/or when there are concerns due to bleeding.
In these instances, you should seek medical advice immediately.
What should I do if I’m told my placenta is low?
Since there’s such a big deal made about where your placenta is, it’s hard to enjoy your pregnancy if you’re worried about what’s going to happen if it doesn’t move.
If you’re told your placenta’s low, first find out from your doctor the distance between the placenta and the os.
Then, ask whether your healthcare provider would be willing to support your wishes for a vaginal birth (if the placenta does not move).
Also, find out what measurement the provider would be happy with, in order to support a vaginal birth.
If you don’t find the support you need, you might decide to seek a second opinion, and possibly change doctor, midwife, or care provider.
There’s nothing you can do to help your womb move up. While you wait for your next scan, focus on supporting your body and baby to be healthy.
Can I have a normal birth with a low lying placenta?
It can be possible to have a normal birth if your placenta is low but it will depend on your doctor or health care provider and their experience.
Doctors’ opinions differ in terms of how close the placenta can be to the cervix when they recommend vaginal birth.
Studies show women with placentas lying lower in the womb are at higher risk of c-section, and that shared decision-making regarding vaginal birth is essential.
If you want to avoid a c-section, it’s useful to have a second or third opinion.
Which week does the placenta move up?
After the 20 week ultrasound, the womb continues to grow quite rapidly, and your placenta usually follows upwards.
It will continue to move away from the cervix, with your growing belly, by week 32 or 36.
There’s no point in worrying yourself crazy, though. Most than likely you’ll be stressing out for nothing!
Does low lying placenta cause pain?
In most instances, if the placenta is low, the most obvious symptom will be vaginal bleeding.
If you have a low placenta, it’s very unlikely it will cause you pain.
It’s very important to remember, though, if you do experience any pain, bleeding, or cramping throughout your pregnancy, you should see your doctor or midwife straight away.
Can you go into labor early with low lying placenta?
In any pregnancy, there’s a risk you can have an early birth.
If this happens you might be offered steroids, between 34-36 weeks, to assist your baby’s lungs to mature more quickly.
Studies show if you’ve had placenta previa before, you’re more at risk of having a preterm birth with your subsequent pregnancy, regardless of where the placenta implants itself.
Giving birth after previous low lying placenta
If you’ve had a low placenta or placenta previa in pregnancy previously, it doesn’t mean it will happen again.
The placenta simply attaches itself where it pleases. In some cases, it’s just bad luck.
“I had a low placenta with my first baby. But my second, third, fourth, and fifth have been fine. PHEW!” – Linda, BB Fan
Low lying placentas resulting in intervention
Here’s a story about a case of a low placenta in pregnancy that needed medical assistance.
“My low placenta was picked up at both the 12 and 18-week scans, but it was never over the cervix, just close. I had no bleeding and didn’t need to take any precautions”.
“The scan at 37 weeks showed that the placenta was still low, but not over. It was about 1.7cm from the cervix when the obstetrician wanted it to be 2cms away. Therefore, I was advised to have an elective c-section at 39 weeks”.
“I tried to research outcomes for labor with that proximity to the cervix, with not much luck, and my obstetrician was a bit dismissive of my efforts to look into it further. So I had the cesarean at 39 weeks”.
“But, in hindsight and after much research, I think I should have sought a second opinion”.
“With no bleeding and a baby that had engaged, I believe I would have been fine for a vaginal birth. At the very least, even my obstetrician acknowledged I would have been okay to go into labor and go from there. There would have only been the need to keep a close eye on how things progressed.
“Allowing labor to start naturally would have been beneficial for my tiny 2.5 kg baby too. She could have done with the extra week or so on the inside, plus the hormones that kickstart birth”.
Remember: If you experience vaginal bleeding at any point in your pregnancy – especially if you receive a diagnosis of the low placenta or placenta previa – you should seek medical advice immediately.
Low lying placenta requiring no intervention
In the vast majority of cases, placenta previa resolves itself and is nothing to worry about.
“I found out I had a low placenta at the 20-week scan, so they booked me in for another scan at 32 weeks. At 32 weeks the placenta had moved a lot – around 7cm, from memory. It continued to move.
“I went into spontaneous labor at 38+5, waters broke around 7.30 am at home and my daughter was born at 3.10 pm. I had no issues at all with my next birth”.
What if my placenta is covering the cervix?
Placenta previa – which means placenta first – is a rare condition that occurs in about 0.5% of pregnancies.
Instead of implanting on the uterine wall, the placenta implants partly or wholly over the internal os.
Although it can happen, the chances are quite low.
If you receive a placenta previa diagnosis in pregnancy, there are more complications to consider as it’s a much more serious condition.