‘Rupture of membranes’ is a term used during pregnancy to describe the rupturing of the amniotic sac. In normal pregnancies, it occurs at the end of pregnancy, either before or during labor, and it is usually not painful. A more colloquial term for ‘rupture of membranes’ is ‘breaking the water’ or also known as one’s ‘water breaking’. When the amniotic sac breaks it results in an increase in production of prostaglandins as well as decreased cushioning between the fetus and the uterus, both of which increase the frequency and the strength of contractions. On occasion if the head is not fully engaged, the umbilical cord may come out of the uterus before or with the fetus, also called a cord prolapse. This is an emergency as the descending head may block the oxygen supply to the fetus; however, luckily it happens in less than 1% of pregnancies. Another complication associated with rupture of membranes is bacterial infection, both in the amniotic fluid and in the fetus.
There are four types of rupture of membranes:
- Spontaneous rupture of membranes – this is when the amniotic sac ruptures at full term
- Premature rupture of membranes – this term describes a rupture of the membranes that occurs before the onset of labor
- Preterm premature rupture of membranes – this describes a rupture of the membranes that occurs before 37 weeks gestation
- Artificial rupture of membranes – this is when your membrane is ruptured by a health professional, such as your midwife or obstetrician, in order to accelerate labor
Spontaneous rupture of membranes
In a spontaneous rupture of the membranes, the rupture is usually over the cervix at the bottom of the uterus and results in a large gush of fluid. The amount of fluid may be quite small, such as 50 ml, but it can also be quite substantial, between 200 and 300 ml. The amount of fluid lost depends on the amount of fluid in the amniotic sac, and to what extent the head of the fetus is plugging the hole and keeping the fluid in the sac.
Preterm premature rupture of the membranes is the leading cause of preterm birth, occurring in 30% to 40% of all preterm deliveries.
Premature rupture of membranes
Premature rupture of membranes may be due to several factors:
- Low body mass index
- Tobacco use
- History of preterm labor
- Urinary tract infection
- Vaginal bleeding during pregnancy
Due to the risk of bacterial infection, you should go to the hospital if labor hasn’t started within 24 hours following rupture of membranes. At the hospital you will more than likely be induced if you are at term.
Preterm premature rupture of membranes
Preterm premature rupture of the membranes is the leading cause of preterm birth, occurring in 30% to 40% of all preterm deliveries. If the pregnancy is between 34–36 weeks gestation, management is the same as for a term pregnancy (induction). If your pregnancy is between 24 and 36 weeks, management includes the following:
- Watchful waiting (expectant management)
- Tocolytic drugs to prevent the beginning of labor
- One-time dose of corticosteroids for the fetal lungs if the pregnancy is fewer than 34 weeks gestation
- Magnesium sulfate infusion for 24–48 hours to allow maximum effectiveness of steroids and also to provide benefit to the fetal brain and gut before delivery
- Antibiotics to prevent Group B streptococcus (GBS) infection if the mother is GBS-positive
Artificial rupture of membranes
To induce or speed up labor, your doctor or midwife may rupture your membranes. This should only be done after your cervix has started to dilate and when the baby’s head is firmly engaged (descended) in your pelvis. This is to reduce the risk of a cord prolapse occurring.
To rupture your amniotic sac, a sterile plastic hook is inserted into your vagina. This usually looks like long crochet hook, or it might be a smaller hook attached to the finger of a sterile glove. The hook is used to pull gently on the amniotic sac until the sac breaks. Following the initial gush of fluid you may still feel some leaking, especially after a hard contraction. This is because the uterus keeps making amniotic fluid up until birth.
Detection of rupture of membranes
There are several ways to test whether your amniotic sac has ruptured. These include the following:
- Fern test: A sterile cotton swab is used to collect fluid from the vagina and place it on a microscope slide. After drying, amniotic fluid will form a crystallization pattern called arborization which resembles leaves of a fern plant when viewed under a microscope
- Nitrazine paper test: A sterile cotton swab is used to collect fluid from the vagina and place it on nitrazine paper. Amniotic fluid is mildly basic (pH 7.1–3) compared to normal vaginal secretions which are acidic (pH 4.5–6.0). Basic fluid, like amniotic fluid, will turn the nitrazine paper from orange to dark blue
- Pooling test: Pooling is when a collection of amniotic fluid can be seen in the back of the vagina (vaginal fornix). Sometimes leakage of fluid from the cervical opening can be seen when the person coughs or does a valsalva maneuver (a type of forced exhalation)
- Ultrasound: Ultrasound can measure the amount of fluid still in the uterus surrounding the fetus. If the fluid levels are low, premature rupture of membranes is more likely. This is helpful in cases when the diagnosis is not certain, but it is not by itself definitive
- Fibronectin and alpha fetoprotein