By Jeyashree Sundaram, MBA

As the gestation period nears completion, the uterus grows to a length of 12 inches (from 3 inches) and the weight increases to 1,100 g (from 30–40 g). The uterus has 5 liters of fluid, and together with its contents the organ may weigh up to 10 kg. This expansion occurs due to the enlargement and elongation of the cells that are available, particularly the (smooth) muscle fibers. These smooth muscle fibers that contract in the myometrium have an effect on the stretching of the uterus.

Image Credit: Antoniodiaz / Shutterstock

True Labor Contractions

During the early pregnancy period, the contractions are short and weak, and may not cause pain.

The placenta releases progesterone, which has an inhibitory effect on the smooth muscles of the uterus and prevents more extensive and powerful contractions. The estrogens produced by the placenta increase the sensitivity of the smooth muscles in the uterus; therefore, contractions are more likely to happen.

The progesterone plays a dominant role throughout the pregnancy period. However, estrogen will dominate when the delivery approaches and myometrium becomes very sensitive to stimulation. The increased oxytocin levels result in increased frequency and force of the contractions in the uterus.

In the endometrium, the production of prostaglandins is stimulated (by oxytocin and estrogens) because of which the smooth muscle contractions are further stimulated.

Each woman experiences contractions differently and it further varies across pregnancies. Labor contractions create pain in the lower abdomen or back, while pressurizing the pelvis and causing discomfort during pregnancy. Pain can also be felt in thighs and in the sides of the abdomen in some cases. Labor contractions are described as strong waves of cramps such as diarrhea cramps or those similar to menstrual cramps.

Braxton Hicks Contractions

Pregnant women may experience Braxton Hicks contractions in the second trimester. Yet, the majority of women come across these contractions during their third trimester. During Braxton Hicks contractions (or practice contractions), the muscles of the uterus will tighten for about 30–60 s or even up to 2 min in some cases. These contractions are actually preparation for true contractions and provide opportunity for women to practice breathing exercises to face true contractions.

Braxton Hicks contractions are not frequent; the intensity of the contraction is not regular and not predictable and the contractions do not follow any rhythm. While some women may feel the pain of contractions, it is largely uncomfortable rather than painful. The contractions may come to an end and may disappear completely. Anyway, Braxton Hicks contractions will ease up.

Some midwives and physicians are of the opinion that Braxton Hicks contractions play a role in toning the uterus muscle and promoting blood flow to the placenta. Though they are expected to play a role in opening the cervix, they might have a role in softening the cervix as well. As these contractions intensify when the delivery time nears, Braxton Hicks contractions are mostly called “false labor.” However, it may help in dilation and effacement of the cervix. In circumstances such as those after sex, when the baby or the woman is very active, if anyone touches the abdomen of the woman, when the bladder is completely filled, dehydration Braxton Hicks may be triggered. Drinking a cup of water or warm milk or herbal tea, taking a shower for 30 min or less, or changing positions can help alleviate contractions.

Differentiating False and True Contractions

The timing and strength of the contractions can help differentiate between false and true contractions.

In true labor, the contractions will start near the top position of the uterus and move in the direction of the cervix, similar to a wave. As the fetus is forcibly expelled in the labor (parturition), while approaching parturition, there will be an increase in the frequency and force of the contractions.

During the beginning of the dilation stage in labor, the contractions are experienced at an interval of 10–30 min and last up to 30 s. The frequency of the contractions will increase gradually.

In the expulsion stage of labor, contractions will happen at an interval of 2–3 min lasting for about 60 s. It is in this stage that the contractions attain their maximum intensity. It is very common that women may moan or grunt as the contractions reach their peak.

While false labor contractions are mostly irregular and they do not get close to one another, contractions in true labor occur at regular intervals and last about 30–70 s. The true contractions get closer as time passes by.

Contractions of false labor may disappear when women take rest or change position, whereas contractions of true labor continue despite changing positions.

If the contractions are due to false labor, the pain is experienced only in the front side, whereas in the case of true labor, the pain begins in the back and moves toward front side.

Further Reading

• All Childbirth Content
• Visitor Policies for Cesarean Sections
• Breeched Birth: Caesarean Section or Vaginal Delivery?
• Natural Childbirth
• What is a Transverse Baby?