The placenta can be inserted into the uterus in different positions: in front of the baby (anterior placenta), behind the baby (posterior placenta), above the uterus (placenta fundica) or on the right or left of the uterus (lateral placenta). In rare cases of a placenta previa, it settles (implants) above the opening of the cervix, in the lower part of the uterus. In pregnancies, an anterior placenta is very common: several studies show that the placenta is positioned in front of the fetus from one third to half of all pregnancies.
Implications of an anterior placenta
The anterior placenta may involve:
- that it may be more difficult to hear fetal movements as the placenta dampens sounds;
- which may be more complicated to perform amniocentesis (a prenatal test)
On the other hand, there are several studies that show that an anterior placenta is not associated with increased risks of pregnancy complications such as hypertension, gestational diabetes or placental abruption.
Movements of the baby in the case of anterior placenta
Most women begin to feel the baby’s movements in their belly between 18 and 24 weeks.
An anterior placenta might make it a little harder to feel your baby move, because its movements are cushioned by the placenta located at the front of the stomach.
Diagnostic tests in the presence of anterior placenta
An anterior placenta can make it more difficult to perform some diagnostic tests, such as amniocentesis: an examination that consists of taking a small amount of amniotic fluid and allows to detect possible alterations of the chromosomes.
An anterior placenta can make this retrieval more difficult, but it is still possible.
There is a small risk of miscarriage after an amniocentesis test, regardless of where the placenta is located, and having an anterior placenta does not increase this risk.
Can the anterior placenta cause complications?
The anterior position of the placenta does not result in a significant increase in pregnancy complications unless pregnancy is in a low position, a condition known as placenta previa.
In that case, the placenta partially or completely blocks the cervix and may result in bleeding.
This condition is most typical in the early stages of pregnancy and may disappear in the course of the process of placental migration and uterine growth.
When a pregnancy is nearing its end, the exact position of the placenta is monitored since any migration to the lower part of the uterus can have relevance regarding the best way to give birth: probably if the placenta is closer than 20 millimeters from the entrance of the cervix (low placenta) or if it covers it (placenta previ) caesarean section will be recommended at 36 weeks of gestation.
Effects on delivery of the anterior placenta
Having an anterior placenta increases the chances that the baby will be in a back-to-back (occipitoposterior) position. If this position is maintained even during labor, the chances of
- a longer labor,
- a more painful labor,
- a cesarean section,
- of having to carry out the birth with a midwife suction cup or forceps.
How do I know if I have an anterior placenta?
The position of the placenta is identified with the second ultrasound, i.e. between week 18 and week 21 of pregnancy.
Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.
She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.