The fetal lie describes the relationship between the longitudinal axis of the mother and the longitudinal axis of the fetus. Three different types of lies are possible: longitudinal, transverse, and oblique lies.

Abstract: The fetal lie describes the relationship between the longitudinal axis of the mother and the longitudinal axis of the fetus. Three different types of lies are possible: longitudinal, transverse, and oblique lies. On the other hand, fetal presentation describes the lowermost part of the fetus or the anatomical structure closest to the maternal pelvic inlet during labor. Fetal presentations are divided into cephalic, breech, shoulder, and compound. Determination of fetal lie and presentation are crucial for appropriate management of the delivery. Using only manual examination, both abdominal and vaginal, diagnosis of fetal lie and presentation is subjective and often inaccurate. Ultrasound is a simple, objective, and accurate tool in the determination of fetal lie and presentation. A systematic approach by the operators is key for such evaluations. We describe in this chapter the various types of fetal lie and presentation, together with respective technique for reliable ultrasound diagnosis.

Keywords: Fetal lie, Fetal presentation, cephalic presentation, breech presentation, ultrasound, intrapartum

Authors: Elena Brunelli1,2, MD, Aly Youssef1,2, MD, PhD

1- Obstetric Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna
2 - Alma Mater Studiorum - Università di Bologna

Reviewers: Karen Fung-Kee-Fung

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Fetal lie

Fetal Lie

The fetal lie describes the relationship between the longitudinal axis of the mother and the longitudinal axis of the fetus. There are three different types of fetal lie:

  • Longitudinal lie,   when both axes are longitudinal and parallel to each other.
  • Transverse lie, when fetal axis is perpendicular to the maternal axis.
  • Oblique lie, when fetal axis is oblique respect to the maternal axis (at about 45 degrees).

Longitudinal lie is the most frequent type, accounting for 99% of pregnancies after 28 weeks’ gestation (1, 2). The oblique lie is usually transient during pregnancy.

Traditionally, Leopold's maneuvers have stood as the standard and sole technique for evaluating fetal lie. (3). However, ultrasound has emerged as a simple, objective and highly reproducible method for determining fetal lie, now recognized as the gold standard. (4).

 

Technique for ultrasound determination of fetal lie

In order to determine the fetal lie, the operator should follow a systematic approach and be able to identify some fetal landmarks to imagine the fetal orientation inside the uterus. The identification of the position of various fetal structures helps the correct and accurate diagnosis of fetal lie. In particular, three easily recognizable fetal structures, can aid the operator to imagine the fetal orientation.

  1. The fetal head: Recognizing the hyperechogenic, oval head is deemed straightforward, even for operators with limited expertise.
  2. Fetal trunk: thorax as identified by the presence of fetal heart, and abdomen by the presence of fetal stomach and/or kidneys.
  3. Fetal pelvis, identified by the presence of the fetal urinary bladder and/or pelvic bones.

 

By following a systematic approach, fetal lie can be depicted. Operators should start by placing the ultrasound transducer in a transverse orientation  on the maternal abdomen at the level of suprapubic region, then move  systematically towards the maternal head, in the midline, till the uterine fundus is reached  and observe the fetal structures they encounter:

  • If the fetus is in longitudinal lie, the three identified fetal structures (head, trunk, and pelvis) will be seen in sequence. In case of longitudinal lie, the order of the visualization of the 3 structures will depend on the fetal presentation (this will be discussed in more details in the fetal presentation section).
  • If the lie is transverse or oblique, neither the fetal head nor pelvis will be seen in the starting position (transverse view in the suprapubic region). The suggested approach in non-longitudinal lies is to look for the fetal head, and then move away, swiping till the fetal pelvis, passing through the fetal trunk. The fetal head will be on the maternal right or left side in case of transverse lie. In case of oblique lie, the fetal head, will be in upper left, upper right, lower left, or lower right quadrants of the maternal abdomen. By depicting the line between the 3 structures (fetal head, trunk, and pelvis), the operator can define the fetal lie. This line will be perpendicular to the maternal axis in the case of transverse lie and will be oblique (midway between longitudinal and transverse lie) in case of oblique lie.

Fetal presentation

Fetal Presentation 

The fetal presentation describes the fetal part that is closest to the pelvic inlet or, in case of labor, is the lowest fetal part in the birth canal. Fetal presentations are roughly divided into:

  • Cephalic presentation: the fetal head is the lowest part of the fetal head closest to the pelvic inlet.
  • Breech: the fetal buttock is the lowest part of the fetal head closest to the pelvic inlet.
  • Shoulder: the fetal shoulder is the lowest part of the fetal head closest to the pelvic inlet.
  • Compound: a combination of more than one fetal structure lies closest to the pelvic inlet.

 

Technique for ultrasound determination of fetal presentation

A systematic approach should be used to determine fetal presentation. Ultrasound scan should start transabdominally in the suprapubic region in the transverse view, and then proceed towards the maternal head in the transverse view. On the basis of the first encountered structure nearest to the maternal pelvic inlet, the fetal presentation is defined.

  • Cephalic presentations are almost invariably in longitudinal lie. Consequently, by following the systematic caudocranial approach, swiping towards the maternal head, operators will sequentially visualize the fetal trunk and pelvis. At term, vertex presentation with anterior occiput is the most frequent cephalic presentation. It is characterized by complete flexion of the fetal head with the fetal chin almost in contact with the chest. According to the fetal head flexion, various subtypes of fetal cephalic presentations exist, which are described in the VISUOG chapter on fetal malpresentations. (5)
  • In breech presentation, the fetal buttock or feet are the closest part to the pelvic inlet (6). In case of breech presentation, by following the same systematic approach as for cephalic presentations, placing the ultrasound probe in the suprapubic region reveals the presence of the fetal buttock and urinary bladder. The swipe of the transducer caudocranially on the maternal abdomen along the midline reveals in order the fetal abdomen, thorax and finally the fetal head.

To determine the subtype of breech presentation, it is necessary to depict the position the fetal spine, femur, and feet. In difficult cases (e.g. deeply engaged breech), transperineal or transvaginal ultrasound can be useful, as they allow the recognition of the fetal lowermost part such as feet or buttock. Subtypes of breech presentation include:

    • Frank breech: both hips are flexed and both knees extended and the feet close to the head.
    • Complete breech: both hips and both knees flexed. In an incomplete breech, one or both hips are not flexed and one or both feet or knees lie below the buttocks.
    • Footling breech: one or both feet are presenting.

Shoulder presentation: this occurs usually in cases of transverse lie, with the back down (dorsoinferior). The fetal head lies on one side of the maternal abdomen and the fetal pelvis on the opposite side, with the fetal spine down.

Compound presentation refers to the presence of more fetal parts entering the pelvic inlet. The most frequent compound presentation occurs in cephalic presentation when the fetal hand is associated with the fetal head. The ultrasound diagnosis of complex presentation is not easy. Transperineal ultrasound can be helpful, as a complementary tool to clinical examination, as it can demonstrate the presence of the various structures presenting in the maternal pelvis.

References

1.         Cunningham FG, Leveno KJ, Bloom SL, Hauth JC, Rouse DJ, Spong CY. Williams obstetrics. 23rd ed. New York: McGraw-Hill; 2010.

2.         Ferreira JC, Borowski D, Czuba B, Cnota W, Wloch A, Sodowski K, et al. The evolution of fetal presentation during pregnancy: a retrospective, descriptive cross-sectional study. Acta Obstet Gynecol Scand. 2015;94(6):660-3.

3.         Superville SS, Siccardi MA. Leopold Maneuvers.  StatPearls. Treasure Island (FL)2023.

4.         Nassar N, Roberts CL, Cameron CA, Olive EC. Diagnostic accuracy of clinical examination for detection of non-cephalic presentation in late pregnancy: cross sectional analytic study. BMJ. 2006;333(7568):578-80.

5.         Bellussi F, Ghi T, Youssef A, Salsi G, Giorgetta F, Parma D, et al. The use of intrapartum ultrasound to diagnose malpositions and cephalic malpresentations. Am J Obstet Gynecol. 2017;217(6):633-41.

6.         Youssef A, Brunelli E, Fiorentini M, Lenzi J, Pilu G, El-Balat A. Breech progression angle: new feasible and reliable transperineal ultrasound parameter for assessment of fetal breech descent in birth canal. Ultrasound Obstet Gynecol. 2021;58(4):609-15.

The article should be cited as: Brunelli E, Youssef A: Ultrasound determination of fetal lie and presentation, Visual Encyclopedia of Ultrasound in Obstetric and Gynecology, www.isuog.org, April 2024. 


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