Common Placenta Positions in Pregnancy

Baby in womb illustration

The placenta is an important organ which facilitates the transfer of oxygen and essential nutrients from the mother to the baby. While it is usually expelled from the mother’s body after birth, it may not happen automatically in a few cases, which is called retained placenta. The umbilical cord connects the placenta to the baby from the mother’s uterus.

What Are the Different Placental Locations?

The placenta, a large pancake-shaped organ, develops during pregnancy, and is attached to the wall of the uterus and can be in different positions. The different possible placental locations are:

  1. Posterior Placenta: When the fertilized egg attaches itself on the back side of the uterus, the placenta develops and starts to grow on the back wall of the uterus. This position of the placenta is known as posterior placenta.
  2. Anterior Placenta: When the fertilized egg attaches itself on the front side of the uterus, the placenta too develops on the front wall of the womb and the baby grows behind it. This position of the placenta is known as anterior placenta.
  3. Placenta Praevia (Low-Lying Placenta): When the placenta grows towards the lower end of the uterus or towards the cervix. This position of the placenta is known as placenta praevia or low-lying placenta.

How is the Location of the Placenta Determined?

The location of the placenta can be determined by carrying out an ultrasound test. Getting an ultrasound done is safe and simple. The nurse will apply a water-based gel on your abdomen and pelvic area, post which an instrument called transducer will be placed on the belly. With the help of high-frequency ultrasound waves, the transducer relays the image of the uterus and also the placenta on a screen.

Does the Placenta Position Change During Pregnancy? 

A placenta occupies a large surface area in the uterus at the beginning of the pregnancy. This reduces considerably as the pregnancy progresses. The placenta can change its position during pregnancy, but it will move either upwards as the baby descends or in very rare cases, downwards, if the baby moves upwards.

What Are the Reasons for Changes in Placenta Position?

As the pregnancy progresses and approaches the third trimester, the head of the baby starts descending into the pelvis in preparation for delivery. The pressure that results from the movement of the head causes the lower section of the uterus to stretch and become thinner. This makes the placenta move upwards.

What Are the Normal Positions of Placenta During Pregnancy? 

In terms of position, the placenta can position itself on the front or back side of the uterus, depending on where the fertilized egg attaches itself after going through the fallopian tube. The placenta then moves upwards during the third trimester, as the uterus prepares for labour. By the last three months of pregnancy, the placenta should be at the top of the womb.

When Should You Worry?

The growth of placenta on the lower end of the uterus or towards the cervix can be a cause for concern. This condition is called placenta previa and it can cause premature labour or internal bleeding due to premature detachment of placenta. Placenta previa may also restrict a normal, vaginal delivery as it will block the cervix. A periodical ultrasound test is done during pregnancy to determine the position of placenta so that the doctors know of any possible complications which may arise due to the position of the placenta.

Woman at doctor

Signs of Low-Lying Placenta

One of the signs of a low-lying placenta could be sudden vaginal bleeding. The other signs and symptoms of a low-lying placenta include:

  • Cramps and sharp pain in the abdomen area.
  • Pre-dominant bleeding during the third trimester of pregnancy.
  • Bleeding after intercourse.

If you observe any of these symptoms continuing for too long, it can be indicative of a low-lying placenta and you should immediately consult your doctor in such a situation.

What Are the Causes of Low-Lying Placenta?

While the exact reason or cause of low-lying placenta is not known, it usually occurs in women who are older, have undergone a C-section delivery before, who smoke or have scars inside the uterus. Women who have suffered from placenta praevia during a previous delivery are also at an increased risk of a low-lying placenta.

In case you have had a low-lying placenta during a previous delivery, the same should be informed to your doctor well in advance.

How Low is Too Low?

In order to determine how far away from the cervix the placenta should be to allow a normal delivery, without affecting the mother or a baby or causing vaginal bleeding, there are following factors which need to be considered:

  • The size of the baby and the amount of space which it will need to get past the birth canal.
  • Whether any fatal blood vessels located below the placenta.

Under normal circumstances, the placenta will not be low lying during birth if the distance between the placenta and the cervix is more than 2 centimetres during the 18-20th week.

If the distance between the two is less than 2 centimetres during the 18-20th week, it may still remain low at the time of birth. Your doctor might ask to get the position of placenta re-checked in the third trimester to determine its position before the delivery.

What Happens If the Placenta is Too Close to the Cervix?

As discussed earlier. if the placenta is too close to the cervix, the mother-to-be is diagnosed with placenta previa. The risks of this condition include premature labour. If the placenta detaches prematurely, internal bleeding. Placenta previa also makes a vaginal delivery difficult. as it blocks the cervix.

Most low-lying placentae correct themselves before the labour and do not cause any hindrance during birth.

The position of placenta plays a very important role in ensuring smooth and safe delivery of the baby. A low-lying placenta or placenta praevia is the only situation where it can cause trouble at the time of labour. Since the reason for a low-lying placenta is not known, it is difficult to prevent it from happening. However, with the help of sonography and ultrasound, the doctors can be aware of the placenta position in advance and take necessary precautionary steps for a safe delivery.

Also Read: Placenta Accreta: Causes, Symptoms Risks & Treatment