What Causes the Water to Break in Pregnancy?

Smiling nurse talking to pregnant woman lying on bed in the hospital
Amniotic fluid cushions and protects your developing baby. (Image: XiXinXing/XiXinXing/Getty Images)

The rupture of your amniotic membranes -- commonly referred to as your "water breaking" -- is a normal part of labor and birth. The "water" is actually amniotic fluid, a straw-colored liquid with a faint odor that may be confused with urine. During pregnancy, this fluid surrounds and protects the developing baby, cushioning her from pressure and concussion.

Spontaneous Rupture of Membranes

Ideally, your waters do not break until labor is well under way. In this case, it is the mechanical force of the contractions themselves that cause the rupture of membranes. If you picture the amniotic sac as a water balloon, labor contractions squeeze the balloon until it breaks at a weak point -- usually at the bottom, near the cervix. If the head of the baby is resting tightly against the mother's pelvis, it may act as a plug, preventing much of the amniotic fluid from escaping.

Premature Rupture of Membranes

In a small percentage of pregnancies -- depending on what source you read, it's about 8 to 12 percent of pregnancies -- the water breaks before the onset of labor, an event called "premature rupture of membranes" or PROM. PROM is usually caused by an infection or by uneven pressure on the membrane from the body of the developing baby. In cases where labor does not begin within 24 to 48 hours after the water breaks, your doctor may choose to induce labor if the baby is sufficiently developed to thrive outside the womb.

Preterm Premature Rupture of Membranes

Preterm premature rupture of membranes or PPROM is a subset of PROM that occurs before the 37th week of pregnancy. The immediate causes are the same as for PROM: infection or mechanical damage to the amniotic sac, leading to a tear that allows fluid to escape. The way your doctor manages the condition depends on several health factors of you and the baby, along with the amount of fluid lost, and the baby's age and level of development.

Risk Factors

Several risk factors predispose a pregnant woman to PROM and PPROM. These include a mother's history of other premature births; a pregnancy with twins, triplets or more; an overproduction of amniotic fluid; an incompetent cervix; an existing infection of the reproductive tract; bleeding during pregnancy; smoking; and inadequate nutrition. Once a woman has had PROM or PPROM, she is more likely to have the same problem during future pregnancies.

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