17. preterm labor and delivery Flashcards
definition of preterm labor?
regular uterine contractions with cervical effacement, dilation, or both before 37 weeks gestation.
definition of preterm birth
live birth between 20 0/7 weeks gestation and 36 6/7 weeks gestation
WHO subcategories: extremely preterm (< 28 weeks), very preterm (28-32 weeks), moderate to late preterm (32-37 weeks).
Classification of preterm birth based on birth weight criteria
extremely-low birth weight (< 1000 g),
very-low birth weight (< 1500 g),
low birth weight (< 2500 g).
preterm birth rate is?
10%
1st trimester weeks
0-4 w’ Pre-embryo
5-12 w’ Embryo
2nd trimester weeks
13-24 w’ Fetus
3rd trimester weeks
25-42 w’ Fetus
Etiologic subgroups of preterm birth
(1) Spontaneous preterm birth (idiopathic) – 45%
(2) Preterm premature rupture of membranes (PPROM) – 25%
(3) Induction of labor for medical indications – 30%
Risk factors for preterm birth
Previous preterm birth
Multiple gestations
Cervical insufficiency
Polyhydramnios
Uterine anomalies
Maternal age (≤ 18 y’ or > 35 y’)
UTIs during pregnancy
Placental disorders
HTN disorders of pregnancy
Smoking
Substance use (alcohol, drugs)
what are the three potential pathways leading to preterm delivery?
(1) Infection-cervical pathway
(2) Placental-vascular pathway
(3) Stress-strain pathway (stress → release of cortisol and catecholamines → placental CRH release → labor)
what prodromal signs may be present for several hours before preterm labor?
- Menstrual-like cramping
- Mild, irregular contractions
- Low back pain
- Pressure sensation in the vagina or pelvis
- Vaginal discharge of mucus, which may be clear, pink, or slightly bloody (mucus plug, bloody show)
- Spotting, light vaginal bleeding
what tests should be performed in case of a preterm labor?
- CBC, serum glucose, serum electrolytes
- Urinalysis, urine culture
- US examination of the fetus → assess fetal weight, document presentation.
May also detect an underlying etiologic factor (ex. twin pregnancy, uterine anomaly).
how do we diagnose preterm labor?
Based upon clinical criteria of regular painful uterine contractions accompanied by cervical changes
Uterine contractions:
≥ 4 every 20 min’ or
≥ 8 in 60 min’
+
Cervical changes:
Cervical dilation ≥ 3 cm or
Cervical length < 20 mm on TVUS or
Cervical length 20-30 mm on TVUS with positive fetal fibronectin
what is a fetal fibronectin?
a protein that attaches the fetal amniotic sac to the uterus
it “leaks” into the vagina if a preterm delivery is likely to occur and can be measured in a screening test
how do we assess the cervical status?
A- cervical funnel length
B- cervical length
C- cervical width
Funneling of the cervix -T, Y, V, U “Trust Your Vaginal Ultrasound”
management of preterm labor
preterm labor after the 34th gestational week should be admitted for delivery.
women with preterm labor < 34 weeks:
1. Antenatal corticosteroid therapy
2. Tocolytics- inhibit uterine contractions and prolong pregnancy.
3. Antibiotics for GBS chemoprophylaxis.
4. Fetal neuroprotection – Magnesium sulfate (For pregnancies at 24-32 weeks of gestation)
Antenatal corticosteroid therapy
- Single course of IM betamethasone/dexamethasone.
- Improves neonatal survival, fetal lung maturity, and surfactant release from type II pneumocytes.
- Indication: < 34 weeks gestation with a risk of delivery within the next 7 days.
- ACOG recommends a single course of betamethasone for pregnant women between 34 to < 37 weeks at risk of delivery within 7 days who have not previously received a course of antenatal corticosteroids.
when are tocolytics indicated in preterm labor?
up to 48 h’ to enable administration of antenatal corticosteroids in preterm labor and/or transportation to another medical center
tocolytics used in preterm labor
- 1st-line agents: NSAIDs (indomethacin) if 24-32 weeks gestation, or Ca2+-channel blockers (nifedipine) if 32-34 weeks gestation.
- 2nd-line agents: β2-agonist (terbutaline), Magnesium-sulphate
what are the indications for Antibiotics for GBS chemoprophylaxis?
preterm labor, PPROM, and/or evidence of GBS infection
Antibiotics for GBS chemoprophylaxis in preterm labor
- 1st-line agents: Penicillin-G (5 million units IV) or Ampicillin (2g IV).
- 2nd-line agents: Cefazolin, Clindamycin, Vancomycin.
what does magnesium sulfate do in preterm labor?
Reduces the risk and severity of neurological disorders (cerebral palsy).
Prematurity puts infants at increased risk of
- Neonatal respiratory distress syndrome (NRDS)
- Intraventricular hemorrhage (IVH)
- Necrotizing enterocolitis (NEC)
- Retinopathy of prematurity (ROP)
- Bronchopulmonary dysplasia (BPD)
- Patent ductus arteriosus
- Neonatal sepsis
- Anemia of prematurity
