The locations of the placenta: anterior, posterior, fundica and previa

When does the placenta form?

The placenta is a temporary organ , which forms a few days after conception and which is expelled after childbirth, in the so-called second stage.

Its origin is twofold, because it arises from a sort of “fusion” between the tissues of the mother and those of the child. For this reason, it consists of two parts:

• a maternal component (called decidua basalis), which develops from the mucosa lining the inside of the uterus
• a fetal component , which originates from the outermost layer of the blastocyst , i.e. the mass of cells from which the embryo will form.

What is the placenta used for?

The placenta connects mother and baby through the umbilical cord and performs essential functions for the fetus:

• it supplies it with the nutrients and oxygen necessary for growth
• eliminates waste substances
• it acts like a filter , preventing the passage of some bacteria, viruses or harmful substances
• produces some essential hormones for the continuation of pregnancy, such as hCG and progesterone

For all these reasons, the health and proper functioning of the placenta is of paramount importance during pregnancy.

Placenta position: when is it normal?

The position of the placenta depends on where the embryo implants itself in the very first weeks of pregnancy. Usually we talk about:

• placenta fundica , when the placenta is located in the  upper part of the uterus , called fundus ;
• lateral placenta , when it inserts on the right or left side ;
• posterior placenta , when it’s placed at the back of the uterus  (between the baby and the spine);
• anterior placenta , when it is located in the anterior part (between the belly and the baby).

These positions are all physiological , although some are more common than others. In some cases, however, it may happen that the placenta is positioned low and completely or partially covers the cervix , i.e. the opening of the uterus. This condition is referred to as placenta previa  and almost always requires a cesarean delivery .

Low placenta does not mean placenta previa!

It is important to note that the observation of a low-lying placenta during first or second trimester ultrasound scans should not be a cause for alarm, as it does not necessarily lead to the development of placenta previa .

Very often, in fact, this organ tends to move upwards as the pregnancy progresses, following the progressive growth of the uterus. For this reason, placenta previa should generally only be discussed after the 28th to 30th week .

Furthermore, also in this case, the diagnosis of placenta previa must be confirmed with an ultrasound in the last weeks of pregnancy , because it is precisely in this phase that the greatest “displacement” of the placenta is witnessed.

Location of the placenta: the fundic placenta and the lateral placenta

The placenta is defined fundic when it is found at the level of the uterine fundus (which, contrary to what the name would seem to indicate, represents the upper part of the uterus, opposite the cervix). This condition is the most common and of no particular concern.

On the other hand, we speak of lateral placenta when the insertion is on the right or left wall of the uterus . This position, although completely physiological, is the one encountered with less frequency .

Location of the placenta: the posterior p lacenta

When the placenta is located at the back of the uterine cavity it is referred to as posterior . This condition allows the mother to better perceive fetal movements and is usually associated with an optimal positioning of the baby for delivery (ie with the back facing the mother’s belly).

Location of the placenta: the anterior p lacenta

The placenta is defined as anterior when it adheres to the anterior wall of the uterus. This position is considered normal and usually does not cause problems for the mother or baby. However it does have some differences from other venues. 

Anterior placenta and fetal movements

When the placenta is in anterior position, it may be more difficult to sense fetal movements , especially when the baby is small. In this case, in fact, the placenta acts as a sort of “cushion” which cushions the movements and makes them perceptible a little later in the course of pregnancy.

In any case, as the child grows, the mother will learn to  recognize his activity . If the fetus should change its usual rhythm and move less than usual , it will be important to contact your gynecologist or midwife .

Also, if you have an anterior placenta, you should avoid using home beat monitoring kits , as they may not be reliable.

Anterior placenta and amniocentesis

The presence of an anterior placenta can make it more difficult to perform amniocentesis , a prenatal test used to diagnose any genetic abnormalities in the fetus.

For this reason, if you choose to perform this exam, it is even more important to contact operators and structures with proven experience , who carry out this routine procedure (such as third-level centres).

What if the placenta subsides?

More rarely, it may happen that during pregnancy the placenta descends slightly instead of moving upwards, partially or totally covering the cervix ( placenta previa ). If this lowering should last until delivery, a cesarean section will almost certainly have to be used to deliver the baby.

In this case, the only difference between the anterior and posterior low placenta is that the former condition may require the incision of the uterus to be made a little higher (for example at fundus level).

Naturally, the gynecologist will choose the best way forward, based on the ultrasound examination .