Post Term Pregnancy and Induction of Labor

Flashcards reviewing post-term pregnancy definitions, risks, management, and methods of labor induction.

How is a post dated (prolonged) pregnancy defined versus a post term pregnancy?

A post dated pregnancy is defined as a pregnancy that extends beyond $41\text{ weeks}$, whereas a post term pregnancy goes beyond $42\text{ weeks}$ of gestation.

What is the incidence rate of pregnancies extending beyond term?

$10\text{ percent}$ of pregnancies will go beyond term.

How does a history of prior post term births influence the recurrence risk in subsequent pregnancies?

$1\text{ previous}$ post term/dated birth leads to a $2\text{ to }3\text{-fold}$ increase in risk, while $2\text{ previous}$ post term/dated births result in a $4\text{-fold}$ increase in risk.

Which fetal disorder is identified as a risk factor for post term pregnancy?

Placental sulfatase deficiency (for example, anencephaly).

What pathological changes in the placenta evidence placental aging and insufficiency in post term pregnancy?

Placental infarcts and calcification, fibrin deposits around the villi, intervillous and arterial thrombosis, and placental apoptosis.

How significantly is the risk of fetal macrosomia increased in post term pregnancy?

Post term pregnancy is associated with a $2\text{-fold}$ increased risk of macrosomia.

What are the key clinical features of postmaturity syndrome (dysmaturity syndrome) in a neonate?

A long, thin body with long nails, minimal subcutaneous tissue, dry, meconium-stained, parchment-like and peeling skin, prominent creases, sparse or absent lanugo, and increased scalp hair.

What percentage of prolonged pregnancies develop postmaturity syndrome?

Postmaturity syndrome is seen in $5\text{ to }10\%$ of prolonged pregnancies.

What is the accuracy of gestational age estimation using a 1st trimester ultrasound scan at $7\text{--}9\text{ weeks}$ versus $10\text{--}12\text{ weeks}$?

The reliability is $\pm 3\text{ days}$ when scanned between $7\text{ to }9\text{ weeks}$, and $\pm 5\text{ days}$ when scanned between $10\text{ to }12\text{ weeks}$.

In a complicated post term pregnancy, what clinical findings indicate immediate delivery?

Delivery is indicated if there is oligohydramnios ($\text{AFI} < 5\,\text{cm}$) or evidence of fetal distress.

In an uncomplicated post term pregnancy, how long is expectant management extended before inducing labor?

Expectant management is extended for $7\text{ to }10\text{ days}$ past the expected date, after which labor is induced.

How is induction of labor defined compared to augmentation of labor?

Induction of labor is the artificial initiation of uterine contractions to accomplish delivery prior to the onset of spontaneous labor. Augmentation refers to the enhancement of existing uterine contractions.

What are five absolute contraindications for the induction of labor (IOL)?

Malpresentations (oblique or transverse lie), cephalo-pelvic disproportion, uteroplacental factors (placenta previa, vasa previa), previous major uterine surgery or classical caesarean section, and active genital herpes or HIV infection.

What Modified Bishop Score threshold indicates a favorable cervix for successful induction of labor?

Out of a total score of $13$, a score of $8\text{ or more}$ is favorable for successful induction, whereas scores less than $6$ indicate an unfavorable cervix that is more likely to fail.

What is the common mechanism of action for mechanical methods of labor induction?

They exert local pressure that stimulates the release of endogenous prostaglandins to promote cervical effacement and dilatation as well as the initiation of uterine contractions.

How is the procedure of stripping the membrane performed?

It is performed by inserting the examining finger through the internal os and moving it in a circular direction to detach the inferior pole of the membranes from the lower uterine segment.

What are the recommended dosage regimens for the three formulations of Dinoprostone (PG E2)?

Vaginal gel: $0.5\,\text{mg}$ intracervically (repeatable after $6\,\text{hrs}$ for $3\text{--}4\text{ doses}$); Vaginal tablet: $3\,\text{mg}$ in posterior fornix (then $3\,\text{mg}$ after $6\,\text{hrs}$, max $6\,\text{mg/day}$); Vaginal pessary: releases $10\,\text{mg}$ over $24\,\text{hrs}$.

What is the intracellular mechanism of action of oxytocin during labor induction?

Oxytocin acts through oxytocin receptors to increase intracellular calcium levels, leading to myometrial contraction, and stimulates amniotic and decidual prostaglandin production.

What is the required waiting period before prescribing oxytocin following the administration of vaginal prostaglandins?

Oxytocin should not be prescribed within $6\text{ hours}$ following the administration of vaginal prostaglandins.

What is the clinical distinction between uterine hyperstimulation and tachysystole as side effects of oxytocin?

Hyperstimulation refers to excessive uterine activity with more than $5\text{ contractions}$ in $10\text{ minutes}$, whereas tachysystole refers to contractions lasting longer than $120\text{ seconds}$.