Preterm labor resident survival guide

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Preterm labor Resident Survival Guide Microchapters

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rinky Agnes Botleroo, M.B.B.S.

Synonyms and keywords:Preterm delivery, Premature labour, Early delivery, Premature birth, Premature labor, Pre term birth


Preterm labor is defined as labor that occurs between after 20 and before 37 weeks of gestation. When preterm labor occurs prior to 33 weeks of gestation, it is called early preterm labor and late preterm labor occurs between 34 and 36 weeks of gestation.Stress, infection, placental abruption, placenta previa, substance use, prior history of preterm birth or abortion, inadequate prenatal care, smoking, maternal age <18 or >40, poor nutrition, low body mass index, fetal anomaly, fetal growth restriction, oligohydramnios, polyhydramnios, vaginal bleeding, premature preterm rupture of membranes (PPROM) are few factors that contribute to preterm labor.It is one of the main cause of neonatal death. Neonates born preterm are at an increased risk of neurodevelopmental disorders, such as cerebral palsy, intellectual disabilities and vision/hearing impairments.Most of the preterm births occur after the spontaneous onset of labor, whereas the rest of the cases are related to maternal or fetal complications, such as preeclampsia or intrauterine growth restriction.


Intra-amniotic infection so far has only been shown to cause preterm delivery.[1] The other factors are being associated based on reports by clinical, epidemiologic, placental pathologic, or experimental studies.Intra-amniotic infections can be subclinical. One in four preterm infants are born due to this cause.[2]


Shown below is an algorithm summarizing the diagnosis of Preterm labor:[9][10]

Abbreviations: BP: Blood pressure; RR=Respiratory rate; HR=Heart Rate, PROM= Premature rupture of membranes; AFV= Amniotic fluid volume

Pregnant woman comes with Preterm labor
Take complete history
Take obstetric history :

❑ Date of last menstrual period.

❑ Estimated date of delivery.

❑ Confirm the gestational age, gravidity and parity.

❑ Check if this is a single or multiple gestation.

Ask about previous obstetric history if she was previously pregnant :

❑ Ask about previous pregnancies including miscarriages and terminations.

❑ Length of gestation.

❑ Ask about mode of delivery.

❑ Ask if there was similar complaints during previous pregnancy?

❑ Was there any complications throughout the pregnancy or during delivery such as shoulder dystocia, postpartum haemorrhage ?

Ask the following questions about menstrual history :

❑ Age of menarche

❑ Last menstrual period.

❑ Is the menstrual flow normal? How many pads she has to use in a day?

❑ Is there any foul smell or colour change?

❑ How many days does the menstruation stay?

Contraceptive history for example oral contraceptives, intrauterine device

Perform physical examination :

❑ A physical exam is done to assess firmness, abdominal tenderness, fetal size, and position.

❑ Perform cervical exam to identify asymptomatic cervical dilatation and effacement.

❑ Regular contractions before term gestational age associated with cervical change, pelvic pressure, menstrual like cramps, watery vaginal discharge, and lower back pain.

Lower back pain is present in normal pregnancy but if it occurs before term, it might be associated with impending preterm labor.

❑ If cervical dilatation is at least 2 or 3 cm at less than 34 weeks, then the patient is highly likely to deliver preterm.

❑ Transvaginal ultrasound may show short cervix( cervical length <25mm at 16-24 weeks of gestation).It can help to distinguish cervical effacement due to cervical insufficiency versus due to active labor.[10]

Do the following tests:

❑ If there is any suspicion about PROM: perform speculum examination to visualize amniotic fluid passing from the cervical canal and pooling in the vagina. Fern and pH testing of the pooled vaginal secretions can indicate rupture of membranes. The pH of amniotic fluid is 7.1 to 7.3.

Fetal fibronectin test[11]: Fetal fibronectin is a protein present between the amniotic membrane and uterine lining. A swab of cervical or vaginal fluid is taken to check the presence of fetal fibronectin. If cervical extracellular matrix breaks, fetal fibronectin will be released. Though it is specific but not a sensitive test. If the result is negative, it is strongly indicates that of an intact membrane, but if positive, it does not necessarily indicative of premature rupture of membranes.

❑ Rectovaginal group B streptococcal culture should be done.

Urine drug screen if mother has history of drug abuse.

❑ A urine culture because asymptomatic bacteriuria increases the risk of preterm labor.

❑ Tests for sexually transmitted infections.



Shown below is an algorithm summarizing the treatment of Preterm labor :[9]

Pregnant woman comes with preterm labor
>34 weeks
<34 weeks
Admit the patient and observe for 4-6 hours
Progressive cervical dilation and effacement
Does not have progressive cervical dilation and effacement
Hospitalise the patient

❑ Perform reactive non-stress test to monitor fetal well being.

❑ Exclude complications of pregnancy.

❑ Send the woman home with instructions to follow-up in 1-2 weeks.

❑ Advise to return to hospital if any sign symptoms of labor arise.

If membranes are intact
If membranes are ruptured
Give tocolytic drugs for up to 48 hours to inhibit labor[12].
Usually pregnancy cannot typically be prolonged anymore for further intrauterine growth and maturation.

If contractions occur even after giving adequate tocolytic therapy, then the physician must reassess the patient for

Amniotic infection

Fetal compromise

❑ Possible abruption

❑ Check if cervix is still changing.

Do the following:

❑ The mother should be sent to a hospital with advanced obstetric and neonatal capabilities for care.

❑ Give proper antibiotics in labor to prevent GBS.

❑ The mother should be given antenatal steroids to to reduce morbidity and mortality of the fetus secondary to respiratory distress.

❑ If preterm labor occurs before 32 weeks of gestation, magnesium sulfate is given for neuroprotection.

❑ Woman should be given appropriate therapy for intraventricular hemorrhage, necrotizing enterocolitis, PDA.


Tocolytics used in preterm labor:

Tocolytic Drug used and special considerations Contraindications
Calcium channel blockers[13] Nifedipine is used as it has fewer side effects. Preeclampsia with severe features

❑ Intrauterine fetal death

❑ Lethal fetal anomaly



❑ Severe maternal cardiac disease

Beta adrenergics Terbutaline[14][15]
COX inhibitors[16] Indomethacin is safest ( should be given no longer than 48 hours due to the risk of PDA closure)
Nitric oxide donors
Weaker tocolytic drugs

Atosiban[17] (oxytocin-vasopressin receptor antagonist) – not available in the United States.
Magnesium sulfate[18] – Most commonly used drug in preterm labor.Physician should be monitoring the mother for the following: Deep tendon reflexes, vital signs, magnesium levels, urine output, and respiratory depression if magnesium sulfate is given to her.
Glyceryl trinitrate[19]



  • If the woman smokes, she should get help to stop smoking before getting pregnant.[4]
  • Heavy physical activity should be avoided.[22]


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  2. 2.0 2.1 2.2 Romero R, Dey SK, Fisher SJ (2014). "Preterm labor: one syndrome, many causes". Science. 345 (6198): 760–5. doi:10.1126/science.1251816. PMC 4191866. PMID 25124429.
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  6. Craigo SD (October 2011). "Indicated preterm birth for fetal anomalies". Semin Perinatol. 35 (5): 270–6. doi:10.1053/j.semperi.2011.05.011. PMID 21962626.
  7. Hossain R, Harris T, Lohsoonthorn V, Williams MA (December 2007). "Risk of preterm delivery in relation to vaginal bleeding in early pregnancy". Eur J Obstet Gynecol Reprod Biol. 135 (2): 158–63. doi:10.1016/j.ejogrb.2006.12.003. PMC 2726845. PMID 17207901.
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  9. 9.0 9.1 "Preterm Labor - StatPearls - NCBI Bookshelf".
  10. 10.0 10.1 O'Hara S, Zelesco M, Sun Z (August 2013). "Cervical length for predicting preterm birth and a comparison of ultrasonic measurement techniques". Australas J Ultrasound Med. 16 (3): 124–134. doi:10.1002/j.2205-0140.2013.tb00100.x. PMC 5029998. PMID 28191186.
  11. Koenn ME (2002). "Fetal fibronectin". Clin Lab Sci. 15 (2): 96–8, 115. PMID 12776771.
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  20. Suhag A, Berghella V (September 2014). "Cervical cerclage". Clin Obstet Gynecol. 57 (3): 557–67. doi:10.1097/GRF.0000000000000044. PMID 24979354.
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