When a diagnosis of preterm labor is suspected and prior to prescribing tocolytics, physicians will make special effort to confirm the diagnosis. Often, transvaginal ultrasonography may be used to exclude the diagnosis of preterm labor based on cervical length. Research of cervical sonography shows that a sonographic cervical length of 18 mm is an optimal positive predictor value, while 30 mm is a negative predictor value.
The presence or absence of fetal fibronectin may also be used as a predictor. Fibronectin is basically a glue that holds the sac to the deciduas. Presence of fibronectin prior to 22 weeks is common. Presence between 22 and 37 weeks is associated with an increased risk in preterm labor, especially in symptomatic women. Fibronectin is typically seen after 37 weeks and indicates readiness to deliver.
Therefore, preterm labor is consistent with cervical length of <18mm, presence of fibronectin and cervical change of 1 cm or more.
Tocolytics are medications used to delay preterm labor, which may reduce neonatal morbidity and mortality.
Maternal contraindications to using tocolytics include hypertension from such sources as eclampsia or chronic hypertension, antepartum hemorrhage, heart disease, sensitivity to medications used for tocolysis, and any medical indication that contraindicates prolongation of the pregnancy. Presumed fetal contraindications for tocolysis includes gestational age >37 weeks, advanced cervical dilation and/or effacement, lethal anomaly, fetal demise, or chorioamnionitis.
The following information is from medical literature and does not necessarily reflect actual patient impressions or experiences:
Magnesium Sulfate has been used as a tocolytic since 1969 and is considered the safest and most commonly used of the tocolytic agents today. Uterine muscles show reduced contractility when the magnesium ion is present, thus reducing excitation of the muscle. Maternal side effects, while few, include flushing, nausea, vomiting, headache, generalized weakness, and shortness of breath. Chest pain and pulmonary edema occur rarely. Since magnesium does cross the placenta, lethargy, hypotonia and respiratory depression may be seen in the neonate.
Indomethacin, given orally or rectally, blocks the pathway for stimulation of uterine muscle contractions ~ it is a prostaglandin inhibitor. Although reported side effects are less than with Ritodrine and Terbutaline, there are still a myriad of side effects, both maternal and fetal/neonatal to cause careful consideration. Maternal side effects include nausea, heartburn, vomiting, gastrointestinal bleeding, alterations in blood coagulation, and asthma in aspirin-sensitive women. Fetal/neonatal side effects include oligohydramnios, neonatal renal insufficiency, reduced fetal urine production, pulmonary hypertension (a potentially fatal situation), necrotizing enterocolitis, small bowel perforation, patent ductus arteriosus, and jaundice.
Ritodrine (Yutopar) and Terbutaline (Brethine, Brethaire, Bricanyl ) are ▀-mimetics that can delay delivery from 48 hours to up to 7 days. Ritodrine is the only agent approved by the FDA as a tocolytic, while Terbutaline not only does not have FDA approval but the FDA disapproves of its use as a tocolytic. These medications cause a relaxation in uterine muscles. Given either subcutaneously or intravenously, ▀-mimetics may produce serious maternal cardiopulmonary and metabolic complications (such as hyperglycemia).
Nifedipine/Procardia and Nicardipine are inhibitors of intracellular calcium entry and selectively inhibit uterine contractions. Their oral administration allows for rapid absorption with a long duration of up to 6 hours. Side effects may include hypotension, rise in pulse, headache, flushing, dizziness, nausea and rise in glucose levels.
The future tocolytics involve oxytocin inhibitors/antagonists such as antocin and an orally active nonpeptidyl oxytocin antagonist, look promising and have few side effects (primarily nausea and vomiting). And the future of diagnostic methods may include the saliva estriols tests.
American Academy of Family Physicians
OBGYN.net Journal Review
New Diagnostics for Preterm Labor
Reeder, S., Martin L., and Koniak-Griffin, D. Maternity Nursing: Family, Newborn and Women's Health Care. 1997. Lippincott.