A 27-year-old woman had daily brown spotting for three weeks from weeks 7 to 10. At 10 weeks, the spotting or bleeding stopped for three days. Then at 10-1/2 weeks, she had red bleeding daily that filled two or three panty liners per day, for a week, followed by two days with no spotting or bleeding. Finally at 11+ weeks she passed two approximately 2 cm diameter clots. Two days after passing the clots, at 12 weeks of pregnancy, she had her first prenatal ultrasound, which showed a live, active fetus of 12 weeks’ size. She filled 3 or 4 pads a day with streaks of brown and red blood for three more days, did not have any bleeding after 13 weeks of pregnancy and went on to deliver a healthy, full-term baby.
Pregnancy ending in first trimester miscarriage is common. Forty-three percent of women who are sexually active and don’t use birth control will report having one or more first trimester miscarriages: 27% reported having had one, 10% two, 4% three, 1.3% four, 0.6% five and 0.05% reported having 6–16 miscarriages (Cohain 2018). Overall, 15% to 25% of pregnancies miscarry, depending on when and how the pregnancy is detected.
In research in which sexually active women not using birth control undergo routine pregnancy tests before they miss a period, 25% of those pregnancies miscarried. Where pregnancy is routinely tested for at four weeks after the last period, 20% of those pregnancies miscarry. Where women undergo pregnancy tests because they suspect themselves to be pregnant—having missed their period—15% of confirmed pregnancies miscarry in the first trimester (Cohain 2018). Second trimester miscarriage is less common. About 1% of those pregnancies miscarry between 15 and 27 weeks (Cohain 2018).
What is usually unappreciated is that many women experience bleeding but do not miscarry. The two large studies of first trimester bleeding show that 25% of women who carry the pregnancy to 28 weeks or more experienced some bleeding in the first trimester (Hossain 2007; Yang et al. 2005). Hossain et al. questioned 2678 pregnant women in the third trimester, and Yang et al. asked 2806 about first trimester bleeding. Axelsen et al. (1995) found a 19% rate of first trimester bleeding when questioning 5868 pregnant women in delivery rooms in Denmark.
About 75% of women with unexplained bleeding report light bleeding for a day or two. “Light spotting” is defined as detection of bleeding by wiping but not requiring use of sanitary protection. Heavy bleeding is bleeding that soaks underwear or requires a pad. Most women experienced a single episode (70%), light spotting (80%) and <4 days total duration (70%), which usually lasted an average of two days (Yang et al. 2005). Women who report light bleeding are less likely to miscarry than those with heavy bleeding. (Women who continue to bleed in the second trimester do tend to have more stillbirths and premature births, especially when the bleeding is heavy.) However, even heavy bleeding in the first trimester does not usually mean miscarriage. Women can be optimistic because 75% of those with heavy first trimester bleeding—defined as heavier than a period—continued the pregnancy to viability (Poulose et al. 2006). There is a very rare phenomenon in which women report having had normal periods during the first trimester of pregnancy at about the time they would expect their menstrual period.
What is known is that most physicians recommend that these women stay in bed, despite the fact that bed rest does not prevent miscarriage. Nonetheless, for lack of anything else to recommend, bed rest is the only recommended treatment.
No study has yet proven why 25% of women with live fetuses experience bleeding during the first 12 weeks of pregnancy. The likely causes of vaginal bleeding vary over the course of pregnancy. Other than miscarriage, the known causes in the first trimester are ectopic pregnancy (1%) and trophoblastic disease (usually a hydatidiform mole) (1 in 1,200 or 0.12%). Causes in the second and third trimesters include incompetent cervix and placenta previa or abruption. Vaginal bleeding at any time can be caused by a vaginal yeast infection, cervical lesion, cervical infection, cervical polyp, systemic disease, cervical or vaginal trauma secondary to sexual activity, sexually transmitted infection, including pelvic inflammatory disease and uterine fibroids. But those causes have symptoms in addition to vaginal bleeding and a medically trained caregiver can diagnose them by taking an accurate history and using visualization, physical exam, bimanual exam, blood tests and ultrasound. However, more than 50% of episodes are of unknown origin (Yang et al. 2005).
In an attempt to link first trimester bleeding with premature birth, several poor quality, retrospective studies asked certain women whether they had had first trimester bleeding—months after the event. One concluded that “[w]omen who experienced vaginal bleeding limited to the first trimester (N=1174) had twice the risk of delivering a preterm infant and 1.6 times the risk of a low birth weight baby compared with those experiencing no bleeding…. first-trimester vaginal bleeding is an important correlate of adverse infant outcomes” (Williams et al. 1991). Hussain repeated this in a 2007 study, which stated that “Women who bled during early pregnancy experienced a 60% increased risk of delivering preterm.”
No logical reason or theory is provided by the authors of these papers for why a day or two of light spotting at 8 weeks might be associated with premature birth at 35 weeks. Premature births occur as a result of inadequate intake of micro- and macronutrients, physical and/or emotional stress and sometimes stressful lifestyle choices such as drugs or smoking, as well as other causes that have not been determined. In the studies that connect premature birth and first trimester bleeding, the reported rates of first trimester bleeding are much lower than the expected 20–25% rate. This means the women studied do not represent the group of women with first trimester bleeding but rather are just a certain small portion of women who had first trimester bleeding. It is more than likely that women with preterm deliveries simply are more likely to recall and report first trimester bleeding; while women with full term births may have long forgotten any first trimester bleeding.
Bleeding in the first trimester generally refers to bleeding after pregnancy has been confirmed, i.e. when the woman knows she is pregnant. Implantation bleeding is given as an explanation for first trimester bleeding, however it occurs before the woman misses a period. After undergoing cell division about every 12 hours, over 2-1/2 days, the microscopic 32-cell blastocyst begins to implant. It is not possible to observe implantation, so no one knows for sure when it actually takes place. Research defines implantation timing by measuring the level of chorionic gonadotropin in the urine (Wilcox, Baird and Weinberg 1999). Using this method, implantation is thought to take place 6 to 12 days after ovulation, although what is actually being measured is the appearance of urinary gonadotrophin, not implantation. In any case, it seems logical to presume that the amount of bleeding from implantation of a microscopic embryo would be microscopic itself and undetectable to the human eye.
Between 8 and 12 weeks of pregnancy, pregnant women with unexplained bleeding who undergo ultrasounds are frequently told that the bleeding is due to a “subchorionic hemorrhage” or “intrauterine hematoma.” This is seen by ultrasound in 5–10% of first trimester pregnancies with unexplained bleeding (Poulose et al. 2006). Subchorionic hemorrhage or intrauterine hematoma, as detected by ultrasound, resolves by itself.
Throughout a full pregnancy, intrauterine hematoma is found by ultrasound among 14% of women. Among the women who were diagnosed as having intrauterine hematoma, 77% carried to full term and did not miscarry (Poulose et al. 2006). Because the condition has no known treatment, diagnosing subchorionic hemorrhage serves no purpose. In addition, prenatal ultrasound has neither been tested nor shown to be safe at the levels of ultrasound currently used and should be used only as medically necessary (Cohain 2012). Also of concern is that once a woman has a diagnosis of a uterine hematoma, the doctor is compelled to send her for additional tests, which will not improve the outcome of her pregnancy (Cohain 2018). Due to the small size of the fetus and placenta, the usefulness of ultrasound in the first trimester is limited to locating the fetus in the uterus, dating the pregnancy and revealing whether the fetus is alive.
The most important thing for women to know is that unexplained first trimester bleeding is usually of no consequence.
- Axelsen, SM, et al. 1995. “Characteristics of Vaginal Bleeding during Pregnancy.” Eur J Obstet Gynecol Reprod Biol 63(2): 131–34.
- Cohain, JS. 2018. “Prevalence of First Trimester Miscarriage among Women with 1 or More Pregnancies of 24 Weeks or More.” J Repr Med, forthcoming 2018.
- Cohain, JS. 2012. “Routine Prenatal Ultrasound Does Not Improve Perinatal Outcomes.” Midwifery Today 102: 46–47, 68–69.
- Harville, EW, et al. 2003. “Vaginal Bleeding in Very Early Pregnancy.” Hum Reprod 18(9): 1944–47.
- Hossain, R, et al. 2007. “Risk of Preterm Delivery in Relation to Vaginal Bleeding in Early Pregnancy. Eur J Obstet Gynecol Reprod Biol 135(2): 158–63.
- Poulose, T, et al. 2006. “Probability of Early Pregnancy Loss in Women with Vaginal Bleeding and a Singleton Live Fetus at Ultrasound Scan.” J Obstet Gynaecol 26(8): 782–84.
- Wilcox, AJ, DD Baird and CR Weinberg.1999. “Time of Implantation of the Conceptus and Loss of Pregnancy.” N Engl J Med 340: 1796–99.
- Williams, MA, et al. 1991. “Adverse Infant Outcomes Associated With First-Trimester Vaginal Bleeding.” Obstet Gynecol 78: 14–18.
- Yang, J, et al. 2005. “Predictors of Vaginal Bleeding During the First Two Trimesters of Pregnancy.” Paediatr Perinat Epidemiol 19(4): 276–83.