Unstable Lie

Unstable lie is a fetal lie that keeps changing between longitudinal, oblique and transverse after 36 weeks of pregnancy, so that the presenting part is different on successive examinations. It matters because labour or rupture of membranes with a non longitudinal lie causes cord prolapse, obstructed labour and uterine rupture, and a cause should be sought.

• Risk factors: grand multiparity (lax uterine wall), polyhydramnios, placenta previa, uterine fibroids or anomaly, pelvic mass, contracted pelvis, prematurity, twin pregnancy.
• A cause is found in some women.
• Safe birth needs admission once labour is near.

Women are usually well, with a uterus that feels wide and a presenting part that differs from week to week or day to day. Fetal heart sounds are heard in different places and the pelvis may feel empty.

• Fundal height smaller than dates with a wide uterus.
• Head felt in a flank or iliac fossa, with an empty lower pole.
• Differential diagnosis: transverse lie, oblique lie, breech presentation, twin pregnancy with one transverse twin, placenta previa, uterine anomaly, fibroid.
• Complications: cord prolapse, arm prolapse, obstructed labour, uterine rupture, fetal death, caesarean section, postpartum haemorrhage.

The diagnosis rests on repeated abdominal palpation and ultrasound at different visits.

• Abdominal examination at each visit from 36 weeks recording the lie and the presenting part.
• Ultrasound: lie, placental site (to exclude previa before any vaginal examination), liquor volume, fetal anomaly, uterine anomaly, fibroids, adnexal mass, estimated fetal weight.
• Cardiotocography; haemoglobin, blood group and Rhesus status.
• Pelvic assessment and a scan at 36 to 37 weeks to confirm persistence.

The principle is to find the cause, admit before labour, and deliver by stabilising induction once the lie is longitudinal or by caesarean section if it cannot be corrected.

• Supportive: avoid vaginal examination until previa is excluded; admit from 37 weeks (or earlier for grand multiparas, women far from the facility, or polyhydramnios); explain warning signs (contractions, leaking fluid, bleeding, reduced movements); two cannulae and group and cross-match when labour starts; knee chest position and bladder filling with sodium chloride 0.9 percent 500 to 750 mL if the cord prolapses.
• Pharmacological: terbutaline 0.25 mg subcutaneous once, 15 minutes before external cephalic version at 36 to 37 weeks; anti-D immunoglobulin 500 IU IM within 72 hours after version for RhD negative women; oxytocin 10 IU in 1 litre Ringer's lactate (10 mU/mL) started at 12 mL per hour (2 mU/minute) and doubled every 30 minutes to a maximum of 192 mL per hour (32 mU/minute) after amniotomy for stabilising induction with the head held over the pelvis (never in a scarred uterus); cefazolin 2 g IV as a single dose before caesarean section; oxytocin 10 IU IM after birth, then 20 IU in 1 litre Ringer's lactate at 125 mL per hour for 4 hours.
• Procedures: external cephalic version at 36 to 37 weeks in a theatre capable facility; stabilising induction at 38 to 39 weeks with the lie corrected by hand, amniotomy when the head is engaged and continuous cardiotocography; planned caesarean section at 38 to 39 weeks if the lie cannot be stabilised; emergency caesarean section for labour or rupture of membranes with a non longitudinal lie, cord prolapse or bleeding.
• Special groups: placenta previa with unstable lie goes straight to planned caesarean section at 36 to 37 weeks and 6 days; a uterine scar has caesarean section instead of stabilising induction; twin pregnancy with a transverse second twin allows internal podalic version with glyceryl trinitrate 400 micrograms sublingual for relaxation.
• Red flags: contractions, leaking fluid, bleeding, cord or arm in the vagina, reduced fetal movements, bandl ring.
• Follow-up: weekly review with a scan for lie from 36 weeks; newborn examination and glucose check if diabetic; review at 6 weeks; counselling that the next birth should be in a facility.