Abnormal labor: Clinical

Abnormal labor is defined as the abnormal onset of labor - either too early or too late in the pregnancy - or abnormal duration of the stages of labor.

Normally, labor onset occurs between weeks 37 and 42 of pregnancies, and labor itself has three stages.

Stage I is when the cervix dilates to 10 centimeters, and it’s divided into a latent phase, covering dilation from 0 to 6 centimeters, and an active phase, when the cervix dilates completely.

Stage II is when the fetus passes through the birthing canal.

If everything goes well, the baby is delivered and labor progresses to stage III, which is the delivery of the placenta.

Ok then! Preterm labor is when regular uterine contractions and cervical changes, which include cervical effacement, or thinning and dilation, start before 37 weeks gestation, but later than 20 or 24 weeks.

Earlier than that, the delivery is called an abortion, because the fetus hasn’t developed enough to survive in the outer world, even with all the neonatal care measured that we have at our disposal.

And the reason we say 20 or 24, is because the OB world is not in full agreement on this matter, either.

Alright - now, risk factors for preterm labor include lifestyle factors, like smoking, alcohol consumption, or illicit drug use, like cocaine or heroin.

Other risk factors include a prior preterm labor, multiple gestation, aka twins or triplets, short cervical length, meaning the cervix is less than 25 millimeters long on ultrasound before 24 weeks gestation, as well as prior cervical surgery, like a cone biopsy that’s done to diagnose or treat cervical cancer.

And then a myriad of other conditions can increase the risk of preterm birth, such as urinary or genital infections, and also obstetric complications like preeclampsia, eclampsia and HELLP syndrome, all of which are associated with hypertension during pregnancy and more, placenta praevia, when the placenta is inserted in close proximity of the cervix, or covers it altogether, or placental abruption, when the placenta prematurely detaches from the uterine wall.