Use of Ultrasonography in Labor and Delivery

Educational Objectives

The goals of this program are to improve obstetric outcomes through the appropriate use of ultrasonography (US). After hearing and assimilating this program, the clinician will be better able to:

1. Use US to augment the evaluation of patients presenting with common obstetric scenarios such as suspected preterm labor, rupture of membranes, abnormal placentation, placental abruption, and nonreassuring fetal heart rate (FHR) tracing.

2. Use US findings to evaluate and advise a patient contemplating vaginal birth after cesarean delivery.

Summary

Preterm labor: incidence of preterm labor (PTL) rising in United States; ultrasonography (US) can distinguish preterm contractions from preterm labor (ie, with transvaginal US examination [TVUS] of cervical length); 80% of patients presenting with preterm contractions not in PTL; studies — among patients between 24 and 36 wk gestation with painful preterm contractions, 37% of those with cervical length <1.5 cm delivered within 7 days, but only one patient with greater cervical length delivered within 7 days; cervical length >1.5 cm has negative predictive value (NPV) of 99%; patients with shortest cervices had highest chance of delivering within 48 hr; among patients with cervical length >2 cm, 5% delivered at <35 wk gestation; in another study, <2% of patients with cervical length >1.5 cm delivered within 7 days, but almost 50% of patients with cervical length <1.5 cm delivered within 7 days; conclusions — cannot exclude PTL with transabdominal examination; only TVUS performed in standardized manner appropriate for identifying PTL; to predict preterm birth, use cervical length at 18 to 24 wk gestation

Premature rupture of membranes (PROM): confirmation of PROM first step in predicting timing of preterm birth; US used to assess integrity of membranes over cervix; studies of patients with PROM in third trimester — when cervix <2 cm long, average latency period 59 hr; when cervix >2 cm long, average latency period 10 days; in patients with preterm PROM, cervical length highly correlated with presence or absence of contractions, based on gestational age

Third trimester bleeding: 3 possible causes — placenta previa or low-lying placenta; separation of placenta; location outside uterus, such as exocervix; use of US — may identify abruption but cannot rule out bleeding from cervix; for suspected placenta previa, begin with transabdominal US to rule out succenturiate lobe with fetal vessels crossing endocervix; scan first with some urine in bladder; if placenta near cervix, empty bladder, then use transabdominal US and TVUS together; placenta previa — previously defined as placenta within 2 cm of endocervix, but recent study showed chance of cesarean delivery (CD) 31% and bleeding rate 3% when placenta 10 to 22 mm from endocervix (if placenta 1-10 mm from endocervix, chance of CD 75% and bleeding rate 29%); discuss options for delivery with such patients

Placental abruption: cannot be reliably diagnosed via US; suggested by clot outside membranes, but clot only visible in ≈50% of cases; site of separation often not visible

Vasa previa: occurs in only 1 in 2500 pregnancies; consider with multiple pregnancy, low-lying placenta in second trimester, in vitro fertilization (IVF; occurs in 1 in 290 patients), or bleeding bilobar or succenturiate placenta; recognition of condition lowers mortality rate

Vaginal birth after CD: rate of CD 33% in United States; identification of patients who should not labor desirable; no uterine ruptures observed when thinnest myometrial diameter ≥2.9 mm, but when wall diameter <2.0 mm, chance of uterine rupture 30%; study — transabdominal evaluation of lower uterine segment (LUS) performed in patients with previous CD; 60% had vaginal delivery; among patients delivered by CD, half of procedures emergent; rate of uterine rupture 2.5% and rate of dehiscence 1.5%; NPV of wall diameter >3.5 mm ≈100%; 16% of patients with wall thickness 1.6 mm to 2.5 mm had scar defect; Montreal study — in patients with previous CD, 9 late uterine scar defects and 3 full-thickness ruptures observed at 36 to 37 wk gestation before trial of labor; receiver operating characteristic (ROC) curve indicated that thickness of LUS <2.3 mm associated with odds ratio of ≈5; history of single-layer uterine closure increased risk 5-fold and interdelivery interval <18 mo increased risk 6-fold (risk highest when all 3 factors present)

Preoperative evaluation: to avoid “surprises,” perform US before every CD; check placental location and fetal position; rule out accreta; determine optimal location of incision for obese patients; determine site of cord insertion

External cephalic version: assessment of amniotic fluid index (AFI) sometimes used to predict probability of successful version; success rate 50% if AFI <10 cm, 51% if AFI 10 to 15 cm, and 64% if AFI high; however, large quantity of fluid may make version more difficult; success rate reasonable even if AFI <10 cm

Nonreassuring fetal heart rate pattern: study — color Doppler with standard US used to evaluate waveform of umbilical vein in 26 patients with pathologic fetal heart rate (FHR) patterns; 26 patients with normal tracings served as controls; presence or absence of umbilical vein pulsations in liver just distal to ductus venosus more useful than evaluating pulsations in amniotic cavity; providers blinded to US findings; 8 patients in pathologic group had pulsations and 75% of these had operative delivery for fetal distress; no patient in control group had pulsations or operative delivery; additional of umbilical vein Doppler waveform may identify true fetal distress in pregnancies with abnormal FHR patterns

Nuchal cord: studies — when found between 17 and 36 wk gestation, outcomes similar to those of matched controls (no differences in gestational age at delivery, rate of CD, nonreassuring FHR prompting CD, FHR abnormalities, meconium staining, or 5-min Apgar); another study found 37% of patients presenting for induction of labor had nuchal cord, but this did not affect need for CD or neonatal outcome; if umbilical cord noted around neck 2 or 3 times, inform and reassure patient, then examine umbilical artery waveform; with impingement of cord, notch sometimes seen in downslope of waveform

Shoulder dystocia: use abdominal diameter as surrogate for shoulder size; find average abdominal diameter or divide abdominal circumference by 3.14, then subtract biparietal diameter from value; final value >2.5 cm reassuring; study found value <2.5 cm to be associated with 33% incidence of shoulder dystocia; repeating this study in 5200 unselected patients showed incidence of shoulder dystocia 25% in patients with index <2.5 cm and 3.8% in other patients

Postpartum hemorrhage: instead of performing curettage, look for retained tissue; if found, remove it under guidance by US

Readings

American College of Obstetricians and Gynecologists: Practice Bulletin no. 116: Management of intrapartum fetal heart rate tracings. Obstet Gynecol. 2010;116(5):1232-40; Andersson O et al: Effect of delayed versus early umbilical cord clamping on neonatal outcomes and iron status at 4 months: a randomised controlled trial. BMJ. 2011;343:d7157; Baenziger O et al: The influence of the timing of cord clamping on postnatal cerebral oxygenation in preterm neonates: a randomized, controlled trial. Pediatrics. 2007;119(3):455-9; Elliott JP et al: Ultrasonic prediction of fetal macrosomia in diabetic patients. Obstet Gynecol. 1982;60(2):159-62; Ennis M, Vincent CA: Obstetric accidents: a review of 64 cases. BMJ. 1990 ;300(6736):1365-7; Hutton EK, Hassan ES: Late vs early clamping of the umbilical cord in full-term neonates: systematic review and meta-analysis of controlled trials. JAMA. 2007;297(11):1241-52; Keith RD et al: A multicentre comparative study of 17 experts and an intelligent computer system for managing labour using the cardiotocogram. Br J Obstet Gynaecol. 1995;102(9):688-700; Lee CY et al: Ultrasonic evaluation of the postpartum uterus in the management of postpartum bleeding. Obstet Gynecol. 1981;58(2):227-32; Mahley S et al: Teaching nursing students to critically evaluate electronic fetal monitor tracings. J Obstet Gynecol Neonatal Nurs. 1999;28(3):237-40; Murray ML, Higgins P: Computer versus lecture: strategies for teaching fetal monitoring. J Perinatol. 1996;16(1):15-9; Perlman JM et al: Part 11: Neonatal resuscitation: 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2010;122(16 Suppl 2):S516-38; Rabe H et al: Early versus delayed umbilical cord clamping in preterm infants. Cochrane Database Syst Rev. 2004;(4):CD003248; Rabe H et al: A randomised controlled trial of delayed cord clamping in very low birth weight preterm infants. Eur J Pediatr. 2000;159(10):775-7; Rozenberg P et al: Ultrasonographic measurement of lower uterine segment to assess risk of defects of scarred uterus. Lancet. 1996;347(8997):281-4; Tsoi E et al: Ultrasound assessment of cervical length in threatened preterm labor. Ultrasound Obstet Gynecol. 2003;21(6):552-5; Tsoi E et al: Sonographic measurement of cervical length in preterm prelabor amniorrhexis. Ultrasound Obstet Gynecol. 2004;24(5):550-3; Vergani P et al: Placenta previa: distance to internal os and mode of delivery. Am J Obstet Gynecol. 2009;201(3):266.e1-5.

Disclosures

In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the planning committee to disclose relevant financial relationships within the past 12 months that might create any personal conflicts of interest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business or commercial interest. For this program, members of the faculty and planning committee reported nothing to disclose.

Acknowledgements

Dr. Hobbins was recorded at the 2012 Annual Clinical Meeting of the Society of OB/GYN Hospitalists, held September 27-29, 2012, in Denver, CO. The Society of OB/GYN Hospitalists will present their next Annual Clinical Meeting September 19-21, 2013, in Denver, CO. For more information, call 713-795-4145, or go to societyofobgynhospitalists.com. The Audio-Digest Foundation thanks the speaker and the sponsors for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

OB600101

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.

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