What Are the Physiological Reasons for Water Breaking During Pregnancy?

Reviewed by Suo Lee, MD

Internal Medicine

Water breaks when the amniotic sac weakens and stretches due to natural changes in the body and the baby's growth, which eventually causes the sac to rupture.

Explanation

The amniotic sac is a thin, protective bag filled with fluid that surrounds the baby during pregnancy. Throughout the pregnancy, this sac slowly becomes more delicate. As the baby grows, the membrane stretches more, and natural enzymes and hormonal changes can gradually weaken it. This process helps prepare the body for labor. When the membranes finally thin enough and are under enough pressure from the growing baby or increasing amount of amniotic fluid, they may break, allowing the fluid to leak out. This is a normal part of the birthing process. In some cases, infections or other issues can make the membranes weaken sooner than expected, leading to a break before labor begins. This explanation shows how natural wear and tear, along with the internal changes in a pregnant woman's body, lead to the rupture of the protective amniotic sac, which is what we call "water breaking.”

(References)

Hadi HA, Hodson CA, Strickland D. Premature rupture of the membranes between 20 and 25 weeks' gestation: role of amniotic fluid volume in perinatal outcome. Am J Obstet Gynecol. 1994 Apr;170(4):1139-44. doi: 10.1016/s0002-9378(94)70109-1. PMID: 8166198.
Moore RM, Mansour JM, Redline RW, Mercer BM, Moore JJ. The physiology of fetal membrane rupture: insight gained from the determination of physical properties. Placenta. 2006 Nov-Dec;27(11-12):1037-51. doi: 10.1016/j.placenta.2006.01.002. Epub 2006 Mar 3. PMID: 16516962.
Wheeler ML, Oyen ML. Premature Rupture of Membranes and Severe Weather Systems. Front Physiol. 2020 May 26;11:524. doi: 10.3389/fphys.2020.00524. PMID: 32528315; PMCID: PMC7264092.
Dayal S, Jenkins SM, Hong PL. Preterm and Term Prelabor Rupture of Membranes (PPROM and PROM) [Updated 2024 Oct 31]. In: StatPearls [Internet].

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