Oxytocin is indicated and approved by the FDA for two specific time frames in the obstetric world: antepartum and postpartum. In the antepartum period, exogenous oxytocin is FDA-approved for strengthening uterine contractions with the aim of successful vaginal delivery of the fetus. There are three situations during the antepartum period in which oxytocin is indicated:

• For mothers who have preeclampsia, maternal diabetes, premature rupture of the membranes
• For mothers with inactive uteri that require stimulation to start labor
• For mothers with inevitable or incomplete abortions in their second trimester

In regards to the postpartum period, oxytocin is FDA-approved when it is time to deliver the placenta during the third stage of labor and also to control postpartum hemorrhage. A former usage of oxytocin in the United States included an intranasal formula that was used to encourage postpartum milk ejection. Other non-FDA-approved indications for exogenous oxytocin include treatment of delayed orgasm, inducing sexual arousal, and treatment of autism. Oxytocin has long been known as a hormone that plays a role in social behaviors and bonding. Because women release oxytocin during sexual intercourse, it is thought to play a role in bonding. Autism is not known to be caused by lower levels of oxytocin when compared to non-autistic people; however, previous studies have shown that giving oxytocin to children with autism seems to spark social skills. Further studies and larger sample sizes are needed.[1][2][3]

Oxytocin is an oligopeptide hormone that contains nine amino acyl residues, or in other words, a nonapeptide hormone. It is one of the two hormones stored and released from the posterior pituitary gland but created in the hypothalamus. It is specifically released from the paraventricular nucleus of the hypothalamus into the posterior pituitary gland for later use. This specific part of the posterior pituitary gland that stores oxytocin is called the pars nervosa, also known as the neural or posterior lobe. Most hormones create negative feedback loops after they are released, but oxytocin is one of the few that exhibit positive feedback loops, i.e., that the release of oxytocin leads to actions that stimulate even more of a release of oxytocin. This feedback is comparable to antidiuretic hormone (ADH), also known as vasopressin (the second and the only other hormone stored and released from the posterior pituitary), which exhibits a negative feedback loop after release. Less of this hormone will be released after it exhibits its effect on the body.

Exogenous oxytocin causes the same response in the female reproductive system as that of endogenous oxytocin. Both types of oxytocin stimulate uterine contractions in the myometrium by causing G-protein coupled receptors to stimulate a rise in intracellular calcium in uterine myofibrils. Oxytocin receptor activation is what causes many signals that then stimulate uterine contraction by increasing levels of intracellular calcium, which is where positive feedback comes into play. When oxytocin is released, it stimulates uterine contractions, and these uterine contractions, in turn, cause more oxytocin to be released; this is what causes the increase in both the intensity and frequency of contractions and enables a mother to carry out vaginal delivery completely. The head of the fetus pushes against the cervix, the nerve impulses from this action travel to the mother’s brain, which activates the posterior pituitary to secrete oxytocin. This oxytocin is then carried through the blood to the uterus to increase uterine contractions further, and the cycle continues until parturition.

Not only does oxytocin stimulate uterine contractions, but it also causes contractions of the myoepithelial cells in the female breasts. This activity occurs in the alveolar ducts. Such contractions are what force milk from these ducts into even larger sinuses, which enable milk expulsion. Positive feedback is also relevant to this milk-ejection reflex. A baby that is attempting to latch on to his mother’s breast signals oxytocin secretion into the blood in the same manner as vaginal delivery; except, instead of uterine contractions, milk is ejected from the breast. The oxytocin makes its way to the brain at the same time to increase more oxytocin secretion.

Lastly, oxytocin also has both antidiuretic and vasodilatory effects, increasing cerebral, coronary, and even renal blood flow.[4][5][6]

An injected form of oxytocin is administered intravenously using the drip method in the setting of delayed and potentially complicated labor. The same route of administration is indicated for both incomplete and inevitable abortions as well. Lastly, in the case of persistent uterine bleeding after giving birth, oxytocin may be given either intramuscularly or intravenously.[7][8]

Common side effects of oxytocin administration include the following: erythema at the site of injection, intensified contractions, more frequent contractions, nausea, vomiting, stomach pain, and loss of appetite. Serious adverse effects that require monitoring after oxytocin administration include cardiac arrhythmias, seizures, anaphylaxis, confusion, hallucinations, extreme increase in blood pressure, and blurred vision.

Specific contraindications to oxytocin include hypersensitivity to the hormone itself or any part of its synthetic version and vaginal deliveries that are in themselves contraindicated. These include the patient having an active genital herpes infection, vasa previa, complete placenta previa, invasive cervical cancer, and prolapse or presentation of the umbilical cord). Other contraindications to administering oxytocin include the fetus in an abnormal position (most notably including a transverse lie) and the fetus exhibiting distress when delivery is not about to happen. Antepartum usage of oxytocin is also contraindicated for women with pelvises not large enough to handle an infant passing through her birth canal, and for when the woman's uterus is either hyperactive or hypertonic.