638 Vertical transmission of human immunodeficiency virus (HIV) is responsible for >90% of pediatric HIV in- fections. The incidence of HIV infection among children is therefore increasing in parallel with the spread of HIV among women of childbearing age. Maternal-infant transmission of HIV-1 may take place in utero, during labor, or postnatally through breast-feed- ing, but the exact contributions of these periods to fetal and infant HIV infections are unclear. The isolation of HIV in vaginal secretions 1, 2 and the exposure of the fetus to maternal blood during delivery support the occur- rence of transmission later during the perinatal period. Other facts that support later transmission are the late de- tection of HIV in infected children, 3-5 the delay in the ap- pearance of acquired immunodeficiency syndrome symp- toms, 6 the increased risk of first-twin infection, 7 and the absence of HIV infection in first- and second-trimester fe- tuses. 5, 8 The main aim of this study was therefore to ob- tain more precise knowledge of the timing of vertical transmission as part of the effort to design strategies to prevent this route of infection. Research into vertical transmission has been delayed because of the difficulty of applying adequate virologic technology capable of detecting a minimum amount of viral load and the relative unavailability of clinical mater- ial from children. The aim of this study was to detect the presence of HIV-1 deoxyribonucleic acid (DNA) in sec- ond-trimester fetal tissues obtained from elective preg- nancy terminations among HIV-1 infected women with the polymerase chain reaction (PCR) amplification tech- nique to further clarify the rate of in utero transmission of HIV. Material and methods Population. Twenty-one pregnant HIV-1–seropositive women seen in the department of gynecology and obstet- rics of the Hospital de Móstoles were studied prospectively. During a 2 1 /2-year period (January 1994–June 1996) thera- peutic abortions were induced by prostaglandin adminis- tration in 21 women. All procedures were second-trimester terminations. Fetal age was determined from the last men- strual period and fetal ultrasonographic measurements. To ascertain the contribution of fetal infection to ver- tical transmission we first had to estimate the rate of ver- tical transmission in our area. Therefore the overall rate of vertical transmission was estimated for the 2 hospitals involved in this study, Hospital 12 de Octubre and Hos- pital de Móstoles, during a 2-year period (January 1994– From the Department of Gynecology and Obstetrics, Hospital de Mós- toles, a and the Departments of Microbiology b and Pediatrics, c Hospital 12 de Octubre. Supported in part by the grant 95/0659 from the Fondo de Investiga- ciones Sanitarias. P. Moreno is a recipient of a Beca de Formación de Per- sonal Investigador grant from the Consejería de Educación y Cultura de la Comunidad de Madrid. Received for publication January 11, 1999; revised January 22, 2000; accepted February 16, 2000. Reprint requests: Ana Pascual Pedreño, PhD, C/Sancho IV, No. 18 13600, Alcázar de San Juan, Ciudad Real, Spain. Copyright © 2000 by Mosby, Inc. 0002-9378/2000 $12.00 + 0 6/1/106591 doi:10.1067/mob.2000.106591 Absence of maternal-fetal transmission of human immunodeficiency virus type 1 to second-trimester fetuses A. Pascual, PhD, a I. Bruna, PhD, a J. Cerrolaza, MD, a P. Moreno, MD, b J.T. Ramos, PhD, c A.R. Noriega, PhD, b and R. Delgado, PhD b Madrid, Spain OBJECTIVE: The aim of this study was to evaluate the contribution of in utero infection to the vertical trans- mission of human immunodeficiency virus type 1 during the second trimester. STUDY DESIGN: We examined fetal tissues from 21 second-trimester prostaglandin-induced abortions among human immunodeficiency virus type 1–infected women and compared the fetal vertical transmission rates with those among children born to human immunodeficiency virus–seropositive women. The presence of human immunodeficiency virus type 1 nucleic acid sequences was investigated with two different highly sensitive polymerase chain reaction techniques in tissue samples from the fetal thymus, lung, and brain. RESULTS: No human immunodeficiency virus type 1 deoxyribonucleic acid was detected in any of the samples. CONCLUSION: The absence of human immunodeficiency virus type 1 in all fetuses in our study is compati- ble with a low rate of maternal-fetal transmission during the second trimester of pregnancy. (Am J Obstet Gynecol 2000;183:638-42.) Key words: Fetal tissues, human immunodeficiency virus, vertical transmission, therapeutic abortion