OBJECTIVE To investigate the operative indication, timing, method, selective standards of feticided fetus and the number of reduced fetuses of selective multifetal pregnancy reduction in second trimester, and the pregnancy outcome of multifetal pregnancy by this operation. METHODS Trans-abdominal selective multifetal pregnancy reductions in 37 cases of multiple pregnancy (twins 6 cases, triplets 21 cases, quadruplets 8 cases, and quintuplets 2 cases) during 12(+1) - 25 weeks were performed under ultrasound guidance. The fetus to be reduced was injected potassium chloride (KCl) intracardiacally until the fetal heartbeat stopped gradually. Totally 46 fetuses were reduced. Periodic prenatal examination and monitoring of coagulation function were carried out after the procedure. The pregnancy complications and pregnancy outcome of all cases were recorded. RESULTS (1) The successful ratio of reduction was 100% (46/46 fetuses) and the successful pregnancy ratio was 88.9% (24/27). (2)Among all the 37 cases, fifteen delivered after 36 weeks, seven delivered in 32 - 36 weeks, three delivered in 28 - 32 weeks, two aborted after feticide, and ten cases were in pregnancy at the time of this study. The mean gestational age of all was (34.9 +/- 4.1) weeks, and the delivery ratio after 28 weeks was 92.6% (25/27). (3) The mean birth weight of singletons was (3014 +/- 640) g, and of twins was (2557 +/- 573) g. The neonates of three triplets all died except for in one case two fetuses were alive. (4) Except in two cases after reducing one fetus of monoamniotic twins, another one died within 24 hours, the remaining fetuses were all alive. (5) Pre-eclampsia occurred in three cases. None of the cases had blood coagulation disturbances. CONCLUSIONS (1) Selective multifetal pregnancy reduction in second trimester can feticide the abnormal fetus objectively or reduce the fetal number effectively. It is a safe procedure to decrease the complications of multifetal pregnancy and increase the birth weight. (2) If the intention is reducing the fetal number, we choose the fetus who lies in the fundus uteri and reduce the multifetal pregnancy to twins. (3) It is advised to aviod performing the procedure during vaginal bleeding. We reduce fetus after vaginal bleeding stops for one or more weeks. (4) Selective second-trimester multifetal pregnancy reduction will not result in the disturbance of blood coagulation and the death of remaining fetus. The incidence of pre-eclampsia is decreased after multifetal pregnancy reduction.