Volume 181, Number 3 Wax et al
Am J Obstet Gynecol
Ultrasonographic diagnosis of thoracopagus conjoined twins in a
monoamniotic triplet gestation
Joseph R. Wax, MD, Denise Royer, RDMS, Joy D. Steinfeld, MD, and Charles J. Ingardia, MD
Hartford, Connecticut
Ultrasonographic examination at 16 weeks 5 days’ gestation diagnosed a monoamniotic triplet gestation com-
plicated by thoracopagus conjoined twins. After pregnancy termination, the ultrasonographic diagnoses were
confirmed by pathologic examination. In reporting the first ultrasonographically diagnosed monamniotic
triplets with conjoined twins, we demonstrate that a systematic evaluation by twin-derived ultrasonographic
techniques may permit correct diagnosis of unusual triplet pregnancies. (Am J Obstet Gynecol 1999;181:755-6.)
Key words: Monoamnionicity, multiple gestation
Higher-order multiple gestations continue to present a nation suggested monoamniotic twins. The pregnancy
challenge for the clinician. Management of these preg- was spontaneously conceived without ovulation induc-
nancies is facilitated by reliable ultrasonographic assess- tion or assisted reproduction. Targeted ultrasonography
ment of chorionicity and amnionicity.1, 2 We report the showed normal amniotic fluid volume and a single ante-
rior placenta. Thoracopagus conjoined twins were ob-
first ultrasonographically diagnosed monoamniotic
served, and this is pathognomonic for a monoamniotic
triplet gestation complicated by a conjoined twin. The
twin gestation. One of the twins was anencephalic,
case shows that when triplet-specific methods of deter- whereas the other had an occipital encephalocele (Fig
mining chorionicity and amnionicity are unsuccessful, 1). They shared a 2-chambered heart and a single umbil-
twin-specific techniques applied in sequence may be di- ical cord. A ventral wall defect was also visualized. Fetal
agnostic. genders could not be determined because of lower-ex-
tremity positions. No dividing membrane was seen sepa-
Case report rating the twins from the third fetus. This triplet was fe-
An 18-year-old woman, para 2-0-0-2, was referred at 16 male and moved freely, ruling out a “stuck” fetus with a
weeks 5 days’ gestation after an ultrasonographic exami- nonvisualized amnion. The anatomic survey was notable
for a hypoplastic left arm and severe kyphoscoliosis.
From the Division of Maternal-Fetal Medicine, Department of Obstetrics Intermingling of fetal parts and umbilical cord entangle-
and Gynecology, Prenatal Testing Center, Hartford Hospital. ment with the conjoined twins were not observed.
Received for publication January 12, 1999; revised February 14, 1999; Thoracopagus twins complicating a monoamniotic
accepted March 16, 1999.
triplet gestation were diagnosed. The pregnancy was ter-
Reprints not available from the authors.
Copyright © 1999 by Mosby, Inc. minated by misoprostol induction of labor. Autopsies of
0002-9378/99 $8.00 + 0 6/1/98607 all fetuses confirmed the ultrasonographic findings.
755
756 Wax et al September 1999
Am J Obstet Gynecol
described a systematic means of approaching twin chori-
onicity and amnionicity. He proposed sequential determi-
nation of fetal gender, the number of separate placentas,
and the presence of the twin peak sign. Same-sex fetuses
with a single placenta and a thin dividing membrane in
the absence of a twin peak sign are consistent with a mono-
chorionic pregnancy. If an intervening membrane is not
visualized under these circumstances, a monoamniotic
pregnancy is suggested. If further study shows no stuck
twin sign or umbilical cord entanglement, monoamnionic-
ity is likely.2 The finding of conjoined twins is pathogno-
monic for a monamniotic twin gestation.
Fig 1. Transverse view through heads of conjoined twins, demon- Conjoined twins complicating a triplet pregnancy al-
strating encephalocele of twin B1 (arrow) and exposed brain tis- though very rare, are well described. Only one reported
sue of anencephalic twin B2 (arrowhead).
case detected prenatally by ultrasonography proved to be
a monoamniotic pregnancy (reference available from au-
thors on request). However, monoamnionicity was deter-
Cytogenetic studies showed all fetuses to be 46,XX. The mined only on pathologic evaluation of the placenta. In
placenta was monochorionic-monoamniotic. reporting the first case of conjoined twins in an ultra-
sonographically diagnosed monoamniotic triplet gesta-
Comment tion, we demonstrate that when a triple-specific method1
The number of triplet pregnancies and the triplet fails to determine membranicity, sequential application
birth rate in the United States have quadrupled from of twin-derived2 techniques may prove diagnostic in un-
1971 to 1994. Management of these higher-order multi- usual triplet gestations.
ple gestations and their related obstetric complications
may be influenced by chorionicity and amnionicity.1 The REFERENCES
few studies specifically addressing ultrasonographic de- 1. Sepulveda W, Sebire NJ, Odibo A, Psarra A, Nicolaides K.
termination of triplet chorionicity and amnionicity rely Prenatal determination of chorionicity in triplet pregnancy by
on membrane thickness at the junction of all 3 gesta- ultrasonographic examination of the ipsilon zone. Obstet
Gynecol 1996;88:855-8.
tional sacs.1, 2 However, not all triplet pregnancies are 2. Finberg HJ. The “twin peak” sign: reliable evidence of dichori-
amenable to diagnosis with this technique.1, 2 Finberg2 onic twinning. J Ultrasound Med 1992;11:571-7.
