The placenta provides nourishment, blood, and oxygen to your baby and is literally what connects the two of you. Problems can occur with either the structure or the placement of the placenta, which may pose a risk to you and to your unborn child.
Uteroplacental Insufficiency (UPI)
Uteroplacental insufficiency occurs when the blood flow and consequently oxygen supply from mother to fetus is impaired or inadequate in some way. This is usually the result of an acute or chronic maternal illness (for example, hypertension, diabetes, preeclampsia, kidney disease), although it can arise from chromosomal abnormalities in the fetus. It may also occur in cases of multiples' gestation (that is, twins, triplets, or more).
Clinical signs that UPI may be present include:
Oligohydramnios. Low levels of amniotic fluid, apparent on ultrasound.
A nonreactive nonstress test (NST). If the fetus is hypoxic (getting insufficient oxygen), its heart rate will not accelerate with (or react to) fetal movement.
Late decelerations in a stress test (or contraction stress test). A slowdown in fetal heart rate that peaks toward the end of a contraction also indicates hypoxia.
Intrauterine growth restriction (IUGR; see above). A fetus that is small for gestational age on ultrasound.
If you are diagnosed with UPI, steps will be taken to correct or treat the underlying cause, if possible. Fetal distress may be cause for immediate cesarean delivery.
A placenta that implants and grows near or covering the cervical opening (or os) occurs in an estimated one of every 200 pregnancies in the second trimester. This condition, called placenta previa, often resolves itself as the uterus enlarges about 90 percent of the time. However, if placenta previa persists late in pregnancy, potentially life-threatening hemorrhage can occur when the cervix starts to efface (thin) and dilate (open).
Placenta previa may be total (that is, completely covering the os), partial (that is, partially covering the os), or marginal (that is, on the margin, or edge, of the os). The condition is diagnosed by ultrasound. Vaginal bleeding is a possible symptom, but some women have no symptoms whatsoever.
If bleeding does occur, bed rest may be prescribed. Blood transfusion may also be necessary. Women who have a placenta previa will usually require a cesarean delivery.
A low-lying placenta is a placenta that is near the os but not close enough to be considered marginal. Like placenta previa, this type of placental implantation has a higher risk of bleeding during late pregnancy.
If you are diagnosed with a low-lying placenta in the first or second trimester, there's a good chance that the placenta will reposition itself as the uterus expands. Because the cervix begins to thin (or efface) during the third trimester, if the placenta remains low in the uterus, hemorrhage becomes a risk. Women who still have a low-lying placenta in the third trimester are usually prescribed bed rest, and a cesarean section may be recommended.
Vaginal bleeding, abdominal cramping, and symptoms of shock (that is, irregular heartbeat, low blood pressure, pale complexion) in the second and third trimesters may indicate that the placenta has begun to prematurely separate from the wall of the uterus, a condition called placental abruption (or abruptio placenta). Risk factors for placental abruption include maternal high blood pressure, cocaine use, or physical trauma to the abdomen.
Abruption may occur anytime after week 20, and if you have had a previous occurrence in an earlier pregnancy, your risk of experiencing it again is increased. Placental abruption may cause major life-threatening hemorrhage, fetal distress or possibly death, and preterm labor. However, a swift diagnosis and initiation of treatment, including blood transfusion, IV fluids, and oxygen, can do much to improve outcomes.
Immediate delivery, possibly by C-section, is indicated in the majority of cases but depends on the stability of both mother and fetus and the length of gestation. In some cases in which only a small segment of the placenta prematurely separates from the uterine wall, careful maternal and fetal monitoring and bed rest may carry a pregnancy safely to term.
Placenta accreta occurs when the placenta implants or attaches to the myometrium (or uterine muscle) instead of to the endometrium. Placenta accreta can be further categorized into two subtypes based on the extent of myometrium invasion — placenta increta and placenta percreta.
In pregnancy complicated by placenta accreta, the placenta does not easily separate from the uterine wall during the third stage of delivery, and postpartum hemorrhage (PPH) occurs. A postpartum blood transfusion, arterial embolization, or an emergency hysterectomy (surgical removal of the uterus) may be required to stop the bleeding and stabilize the patient.
If you are diagnosed with this condition prior to delivery, it's important to discuss the possibility of a hysterectomy. In many clinical situations, a hysterectomy may be unavoidable, but if an option is available, your doctor needs to know of any desire for more children so she can preserve your fertility if at all possible.
According to the ACOG, the incidence of placenta accreta has risen dramatically in the past fifty years and currently happens at a rate of one in every 2,500 deliveries. This increase can probably be traced to the climb in cesarean section rates; placenta accreta is more likely to occur in women with a history of cesarean delivery (and climbs with each subsequent C-section). In addition, women who are diagnosed with placenta previa have a substantially increased risk of placenta accreta.
If you are considered at risk for the condition, magnetic resonance imaging (MRI) and ultrasound may be used to confirm a diagnosis. A high alphafetoprotein (AFP) level may also be a sign of placenta accreta.