A gynecologist is devoted only to the reproductive care of women while an obstetrician is concerned with women during and a little after pregnancy. Obstetricians are also concerned with the health of the fetus. Almost all modern Gynecologists are also Obstetricians.
Gynecologists offer preventive reproductive health care and treat diseases, while obstetricians deliver babies and care for mother and baby during post-delivery.
In addition to performing regular breast exams, mammograms and pap smear, gynecologists treat fertility problems, deal with contraception, tubal ligations and hysterectomies. They also deal with uterine and vaginal infections or diseases. The diseases they typically encounter are cancer of reproductive organs (ovaries, uterus, fallopian tubes, cervix, vagina and vulva), incontinence, amenorrhea (absent menstruation), dysmenorrhea (painful menstruation), infertility, menorrhagia (heavy menstruation), prolapse of pelvic organs, fungal, bacterial, viral or protozoal infections to reproductive organs. The gynecologist will usually confirm that a woman is pregnant and then refer her to an obstetrician.
Obstetricians do not treat diseases of the reproductive organs. They deal with any complications during childbirth such as ectopic pregnancy (embryo in fallopian tubes), fetal distress (fetus is compressed in the uterus), pre-eclampsia (convulsions due to hypertension), placental abruption (patient can bleed to death if not properly managed), shoulder dystocia (one of the fetus' shoulders becomes stuck during birth), uterine rupture, prolapsed cord (causes a risk of fetal suffocation), obstetrical hemorrhage and sepsis (infection of uterus before or after childbirth).
See also Doula vs Midwife.
Some of the typical procedures performed by a gynecologist are hysterectomy (removal of the uterus), oophorectomy (removal of ovaries), tubal ligation (as a form of contraception), laproscopy, laprotomy, cystoscopy and pap smear (to identify pre-cancerous cells).
Obstetricians usually perform vaginal or cesarean deliveries.
These days almost all gynecologists are also obstetricians, and most obstetricians also practice gynecology.
Obstetrics and gynecology are often combined to form a single medical specialty in post-graduate medical training, abbreviated to OB/GYN. But any complications with the baby after delivery is treated by neo-natal specialists. Training in this specialty in the U.S takes 4 years after 4 years of medical school (D.O. or M.D.) is completed. Australia has the longest training period with 6 years. In India, after 5 years of MBBS and a year of internship, a postgraduate diploma in OB/GYN takes 2 years and an MD takes 3 years. Some choose to pursue a fellowship which can take from one to 4 years and has a research component.