Losing the mucus plug during pregnancy

By trimester

Weeks 1–13

1st trimester

The mucus plug forms early, as thick cervical mucus builds up and seals the cervical canal. Noticeable discharge this early isn't the labor-related mucus plug loss people mean later in pregnancy, so mention any unusual discharge to your provider rather than assuming that's what it is.

Weeks 14–27

2nd trimester

The mucus plug is still doing its job of sealing off the cervix through the second trimester. True mucus plug loss as a labor sign is mainly a third-trimester event, so it's uncommon to lose it now.

Weeks 28–birth

3rd trimester

This is when losing the mucus plug becomes a relevant sign that your cervix is starting to change. It can happen days before labor or right as it starts, especially with a first baby, and because effacement is often gradual, it's common to notice it in stages rather than all at once.

What does the evidence show for losing the mucus plug?

• The cervical mucus plug forms from thick mucus secretions that build up in the cervical canal and act as a protective barrier limiting how much bacteria from the vagina can reach the uterus during pregnancy. 1
• Loss of the mucus plug, sometimes along with a small amount of blood-tinged mucus known as bloody show, can happen as the cervix begins to efface, often before true labor starts, and this is especially common with a first baby. 2
• Research measuring the mucus plug's makeup has found its inflammatory markers shift with gestational age, with certain markers running several-fold higher in plugs collected around preterm labor compared with plugs collected at term. 3
• NICHD lists changes in vaginal discharge, including leaking fluid or bleeding, among the warning signs of preterm labor before 37 weeks, alongside regular contractions, pelvic pressure, and low backache. 4
• Foul-smelling vaginal discharge is one of the clinical signs of chorioamnionitis, a uterine infection that also typically involves fever, uterine tenderness, and a faster than normal heart rate in mother or baby. 5

When should I call my provider about losing the mucus plug?

Losing the mucus plug before 37 weeks is one of the vaginal discharge changes NICHD lists among preterm labor warning signs, especially alongside contractions, pelvic pressure, or fluid leaking, and is worth a same-day call to your provider. Discharge that looks green or smells foul points toward a possible infection such as chorioamnionitis, which also tends to involve fever, uterine tenderness, or a rapid heart rate, rather than routine mucus plug loss, and also needs prompt evaluation. If you are ever unsure which side of the line you are on, make the call. Obstetric teams handle these check-ins as routine, not as overreacting.