258 with a lower rate of induction of labor for post-term pregnancy. There were seven major fetal abnormalities in the USS group (four with neural tube defects, one with proven trisomy 18, one with probable trisomy 21, and one with multicystic renal dysplasia), and three in the control group (tetralogy of Fallot, cleft lip, and amniotic band syndrome). Only one pregnancy, with a neural tube defect, was terminated. In this study, routine second-trimester ultrasound scanning was not associated with substantive changes to obstetric care or pregnancy outcome. Areas of potential benefit were reduction in the rate of post-term inductions, resolution of uncertainty with menstrual dating, and the possibility of pregnancy termination for major fetal abnormality. The study sample was insufficient to provide conclusive results with respect to morbidity in twin pregnancies or perinatal death. However, the results do not contradict previously published findings [2–4]. High priority can therefore not be given to provision of routine pregnancy ultrasound screening in poorly resourced settings. Careful clinical assessment
BRIEF COMMUNICATIONS remains the cornerstone of pregnancy care, with ultrasound being a useful adjunct.
References [1] Department of Health. Guidelines for maternity care in South Africa. A manual for clinics, community health centres and district hospitals. Pretoria: Department of Health; 2002. [2] Ewigman BG, Crane JP, Frigoletto FD, LeFevre MD, Bain RP, McNellis D. Effect of prenatal ultrasound screening on perinatal outcome. RADIUS Study Group. N Engl J Med 1993;329:821-7. [3] Geerts LT, Brand EJ, Theron GB. Routine obstetric ultrasound examinations in South Africa: cost and effect on perinatal outcome — a prospective randomised controlled trial. Br J Obstet Gynaecol 1996;103:501-7. [4] Neilson JP. Ultrasound for fetal assessment in early pregnancy. The Cochrane Database of Systematic Reviews 1998, Issue 4. Art. No.: CD000182, DOI:10.1002/14651858.CD000182.
Transabdominal and transvaginal ultrasonography of placenta previa K. Lahoria, S. Malhotra, R. Bagga ⁎ Department of Obstetrics and Gynecology, Postgraduate Institute of Medical Education and Research, Chandigarh, India Received 20 March 2007; received in revised form 26 April 2007; accepted 26 April 2007
KEYWORDS Transabdominal sonography (TAS); Transvaginal sonography (TVS); Cesarean delivery; Vaginal delivery; Internal os–placenta distance
Transvaginal sonography (TVS) images the cervix precisely and is widely preferred to transabdominal sonography (TAS) in detecting placenta previa. Although some studies have correlated the internal os–placental distance with ⁎ Corresponding author. Department of Obstetrics and Gynecology, Postgraduate Institute of Medical Education and Research, Sector 12, Chandigarh, 160012, India. Tel.: +91 172 275 6349; fax: +91 172 274 4401. E-mail address:
[email protected] (R. Bagga). doi:10.1016/j.ijgo.2007.04.024
mode of delivery, it is not clear at what distance the placenta should be considered low lying, or what the appropriate mode of delivery should be with respect to this distance [1,2]. In this prospective study, TVS and TAS were compared in 90 women with placenta previa and the os–placental distance was compared with mode of delivery. Women with antepartum hemorrhage (APH) attributed to placenta previa, or placenta previa observed during routine sonography, were included. Women with severe bleeding, abruptio and indeterminate APH were excluded. All underwent TAS with partially full bladder followed by TVS after voiding (3.5, 5– 7.5 MHz, ATL 1500). Placental location (covering os, marginal or low-lying) and os–placental distance were noted. At delivery, this distance was assessed by digital examination or per the operative findings. As it is not possible to measure the exact distance during a cesarean section, the surgeon's assessment was accepted. The women were classified into 4 groups: I (placenta covering os or ≤2.0 cm from os); II (2.1– 3.5 cm from os); III (N3.5 cm from os); and IV (sub-optimal view). Scans were repeated every 2 weeks and the last scan was considered for analysis.
BRIEF COMMUNICATIONS Table 1
259
Distance from placental edge to internal os and mode of delivery
Groups based on TVS
Group I (covering os or ≤ 2.0 cm from os) Group II (2.1–3.5 cm from os) Group III (N 3.5 cm from os) Totals
No. of women
Elective cesarean
Emergency cesarean Total
Low placenta in labor
APH
Obstetric complications⁎⁎⁎
72 13 5 90
24 – – 24
48 10 – 58
6⁎ 2⁎⁎ – 8
35 4 – 39
7 4 – 11
Vaginal delivery – 3 5 8
⁎All 6 had placenta covering the os with prior episodes of bleeding. ⁎⁎Labor was induced (intrapartum bleeding), os–placental distance was 2.2 and 3.3cm. ⁎⁎⁎For Group I these were: breech with ruptured membranes; twins with T1 breech in labor; bad obstetric history with chronic hypertension and diabetes; poor biophysical profile; severe pre-eclampsia with absent end diastolic flow; and non-reassuring CTG in 2 women. In Group II these were: growth restriction with poor biophysical profile; triplets in labor; and breech with ruptured membranes in 2 women.
Mean gestation at last scan was 35 ± 2.9 weeks (range 28–40); delivery interval from last scan was 4.7 ± 5.4 days (range 0–14); 67/90 (74.4%) were symptomatic; and gestation at delivery was 35 ± 2.9 weeks (range 29–40). Precise os–placental distance could be measured in all cases (100%) by TVS and in 82/90 (91%) by TAS. Correct diagnosis was made in 87/90 (96.6%) with TVS and 73/90 (81.1%) with TAS. There were 28, 6 and 56 women with anterior, central, and posterior placenta, respectively. TVS was most accurate in detecting posterior placenta as it correctly diagnosed 55/56 versus 43/56 by TAS. Based on TVS groups, 72/72 (100%) in group I, 10/13 (77%) in group II, and 0/5 in group III delivered by cesarean (Table 1). All the women with a placenta b2.0 cm from the internal os required cesarean delivery, while those with a placenta N 3.5 cm delivered vaginally. When os–placental distance was 2.1–3.5 cm, vaginal delivery was possible; however, careful monitoring with facilities to perform emergency cesarean is necessary. These results are similar to earlier studies that support the accuracy of TVS over TAS, especially in posterior placenta [3,4]. A retrospective analysis of 52 women where TAS and TVS were performed 5 weeks prior to delivery observed that 31 women with total previa and 7 with an os–placental distance of 1.1 ± 0.8 cm (range 0–2 cm) underwent cesarean; 14 women with an os–placental distance of 3.1 ± 1.1 cm (range 1.8– 5.8 cm) delivered vaginally [1]. Another study observed that vaginal delivery was safe with an os–placental distance of N 2.0 cm, that vaginal delivery was an option with careful monitoring between 1 and 2 cm, and that cesarean was needed if b 1 cm; however, these scans were performed 6weeks prior to delivery [2]. In an analysis of 121 women with a mean scan to delivery interval of 10.5 days, cesarean rate was 90% and 37% when the os–placental distance was b 2.0 cm and N 2.0 cm, respectively [5]. The time interval between ultrasound and
delivery may influence the os–placental distance. “Placental migration” of 0.54 cm per week in the third trimester is reported [6]. Based upon this, with a mean of 4.7 days between the last scan and delivery, the placenta is unlikely to have been displaced N 0.4 cm in the present study. The distance from the internal os to the placenta for a diagnosis of placenta previa has been arbitrarily selected as 5.8 cm, 3.0 cm and 3.5 cm by various authors [1,2,6]. In the present study, the maximum os to placental distance was 5.8 cm, and the results suggest that a distance of N 3.5 cm from the internal os need not be considered previa.
References [1] Oppenheimer LW, Farine D, Ritchie JW, Lewinsky RM, Telford J, Fairbanks LA. What is a low-lying placenta? Am J Obstet Gynecol 1991;165:1036-8. [2] Dawson WB, Dumas MD, Romano WM, Gagnon R, Gratton RJ, Mowbray RD. Translabial ultrasonography and placenta praevia: does measurement of the os–placenta distance predict outcome? J Ultrasound Med 1996;15:441-6. [3] Leerentveld RA, Gilberts EC, Arnold MJ, Wladimiroff JW. Accuracy and safety of transvaginal sonographic placental localization. Obstet Gynecol 1990;76:759-62. [4] Sherman SJ, Carlson DE, Platt LD, Medearis AL. Transvaginal ultrasound: does it help in the diagnosis of placenta previa? Ultrasound Obstet Gynecol 1992;2:256-60. [5] Bhide A, Prefumo F, Moore J, Hollis B, Thilaganathan B. Placental edge to internal os distance in the late third trimester and mode of delivery in placenta praevia. BJOG 2003;110:860-4. [6] Oppenheimer L, Holmes P, Simpson P, Holmes N, Dabrowski A. Diagnosis of low-lying placenta: can migration in the third trimester predict outcome? Ultrasound Obstet Gynecol 2001;18:100-2.
