Here, we’ll focus on the basic physical nature of labor.

Preterm Labor

A woman is in preterm labor, also known as premature labor, if she begins having regular contractions (no Braxton-Hicks contractions) that causes her cervix to start to open or thin out (called dilation and effacement) before 37 weeks of pregnancy. Birthing a baby before 37 weeks may require a stay in the NICU or neonatal intensive care unit.

Prodromal Labor

Often the diagnosis of prodromal labor or prolonged Latent Phase of labor is made retrospectively.  “False Labor” or persistant Braxton Hicks contractions should be ruled out, as well as cephalopelvic disproportion and other malpresentations.  Prodromal labor is persistant contractions with no signs of cervical progress, no change in the station and no change in maternal emotions, other than frustration at the lack of progress.  According to the World Health Organization, “misdiagnosing false labour or prolonged latent phase leads to unnecessary induction or augmentation, which may fail.  This may lead to unnecessary caesarean section and amnionitis.”

Prelabor Signs

"Lightening," which refers to the baby's head dropping and settling into the pelvis, can occur anywhere from a few hours before labor to a few weeks before labor. Older relatives/friends may use the term dropping although this does not mean that the mother will feel or notice the baby settling down. The process of lightening is a slow one and may only be noticed by those who do not see the mother very often.

Blood-tinged mucous, or "show," is often a sign that the cervix is beginning to dilate. There should never be large amounts of blood at any time. The bloody show refers to the glob of mucus that fits like a cork inside the opening of the cervix - it acts as a barrier to infection. It may come out all at once or it may come out gradually, in which case the expectant mother may not be able to distinguish it from the increase vaginal discharge of late pregnancy.

The cervix will thin or efface and soften, dilating to 10 centimeters and effacing to 100% by the end of the first stage. The bag of waters or amniotic membranes may rupture in the first stage of labor by themselves, releasing the amniotic fluid that surrounded the baby in the uterus. If the membranes break high in the uterus, expectant mothers may only notice a consistent trickle of fluid. And if the membranes break low toward the opening of the cervix, she may feel something like champagne popping between her legs, then a gush of warm odorless and colorless fluid. Care providers should be contacted immediately if the expectant mother think her membranes have ruptured. Contacting her caregiver is especially important if there is meconium in the amniotic fluid. Meconium is the baby's first bowel movement and will color the amniotic fluid (which, again, is typically odorless and colorless) so that it looks like green pea soup.

Timing of Labor: Friedman’s curve

Much of the diagnostic reference for timing of labor is associated with the Friedman Labor Curve. For the past half-century obstetric practice has followed the description of normal labor set out in a landmark, 500 person study by Dr. Emanuel Friedman.

Friedman established the following definitions of labor progression in 1955:

* Latent Phase – about 12 hours
* Active phase – about 5 hours
* Transition – about 2 hours

Obviously much more is known about labor and birth now than 50 years ago.  The expectant parent is much more educated, allowing for more instinctual birthing methods that cooperate with the body rather than fighting against.  Fighting against the body’s natural birthing progress can be the source of fear and tension and result in the release of stress hormones (adrenaline) which systematically counteracts the very hormone that helps initiate labor – Oxytocin.

Stage 1 – complete dilation and effacement.  During this time the baby completes the cardinal movements and completes descent into the pelvis.  The descent of the baby through the pelvis is measured in terms of pelvic station – or the relationship of the fetal head to the ischials spines of the pelvis.  Three great references for showing pelvic station are the Pelvic Station Chart ; The Female Pelvis Book and a “real” pelvis with which to teach.

*It is important to note that effacement does not follow any particular pattern and the thinning process may be complete before the dilation is complete.

Latent Phase – usually the longest phase, where the cervix dilates from 0-3 cms., and contractions are typically 30-45 seconds in duration and about 5-30 minutes apart.

Active Phase – the cervix dilates from 4 – 6 cms and contractions may be 60 seconds in duration and about 3-5 minutes apart.

Transition – one of the shortest phases but one where the contractions will not get any harder, they just get closer together.  Contractions may be 90 seconds in duration and about 1-3 minutes apart.

Stage 2 – begins with complete dilating and effacement and ends with birth of the baby.  Contractions here are now 60 seconds in duration and may be about 3 minutes apart.  There may be a resting period between complete dilation/effacement and the onset of the urge to push.  Famed childbirth educator Sheila Kitzinger calls this the rest and be thankful stage.

Stage 3 – begins with birth of the baby and terminates with the birth of the placenta.  The contractions associated with birthing the placenta may not even be noticeable to the mother who is rightfully euphoric about the birth of her child.

Stage 4 – begins with the birth of the placenta and extends to the first 2 hours postpartum.  Mild “afterbirth” contractions may be annoying but manageable.