The biggest difference in heart rate between pair of twins was found between 6 and 7 weeks of pregnancy. Later in pregnancy up to 11+6 weeks the difference was similar and remained low.
Two Distinct Heartbeats are Heard
With careful listening, a doctor or midwife can sometimes detect multiple distinct heartbeats and might suspect that there are twins. If so, an ultrasound scan can provide confirmation.
A normal resting heart rate is about 70 bpm (beats per minute), rising to 80-100 bpm in pregnancy. People who are pregnant with twins or multiples may have a resting heart rate higher than 100 bpm. If your resting heart rate is above 100 bpm, you may be diagnosed with tachycardia.
Multiples do tend to be born smaller than single babies. But it's not because their growth rate is necessarily slower — in fact, for twins, it's about the same as any other baby's until about weeks 30 to 32, when they do slow down a tad, since they're competing more for nutrients.
By 6 weeks, their hearts are beating, and at 8 weeks all of their major organs start developing. The twins' faces take shape, with closed eyelids, at 12 weeks, and at 16 weeks their sex organs are apparent.
In a typical identical twin pregnancy, an egg splits during its first week after fertilization. But in a mirror twin pregnancy, the egg splits 7 to 12 days after it's been fertilized — long enough for the egg to have developed a right and a left side.
Most first-time moms of twins don't feel fetal movement, or quickening, until 18 to 20 weeks — about the same average for singletons. That said, if this is your second or later pregnancy, you're more likely to feel the flutterings faster.
As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood.
Factors that increase the chance of twins include: consuming high amounts of dairy foods, being over the age of 30, and conceiving while breastfeeding. Many fertility drugs including Clomid, Gonal-F, and Follistim also increase the odds of a twin pregnancy.
Early signs of a twin pregnancy include severe morning sickness, quick weight gain, and more breast tenderness. You may also notice an increased appetite or extreme fatigue. Plus, those who have a twin pregnancy may begin showing sooner.
The most reliable method of confirming a twin pregnancy is prenatal ultrasound. This test uses sound waves to produce images of your uterus. Ultrasound makes it possible to see whether there are two fetuses.
At eight weeks, your twins' hearts have divided into right and left chambers, and will soon have all four chambers. They're already beating at about 150 beats per minute. This is twice as fast as your own heartbeat.
Gestational Age Week 7 (Fetal Age: 5 weeks)
Generally, from 6 ½ -7 weeks is the time when a heartbeat can be detected and viability can be assessed. A normal heartbeat at 6-7 weeks would be 90-110 beats per minute. The presence of an embryonic heartbeat is an assuring sign of the health of the pregnancy.
If you're pregnant with a single baby and think you hear two heartbeats, you're likely hearing echoes. Some people hear two noises and think they're pregnant with twins. Unless your doctor has confirmed multiple pregnancies, it's likely you're hearing the echo of your single baby.
How soon can you tell you're pregnant with twins? Your doctor won't be able to tell for sure until your first trimester ultrasound, which is usually done between 6 and 9 weeks of pregnancy but can be done any time between week 14.
However, for a given pregnancy, only the mother's genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father's genes can't make a woman release two eggs.
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.
After all, most new parents have their hands full with just one baby! The reality is that raising multiples is hard. You have double or triple the feeding, diapering, and laundry and, as a result, less time to spend cuddling and getting to know each baby.
Birth Order and Twins
The babies' order of birth is determined by their position in the womb, which can change throughout pregnancy. In some cases, which baby is born first depends on how the mother delivers; the order might be switched if the mother had a Cesarean section rather than vaginal delivery.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA.
Twins and triplets often don't have a chance to reach a healthy weight before they're born. While the average single baby weighs 7 pounds at birth, the average twin weighs 5.5 pounds. Triplets typically weigh 4 pounds each, and quads weigh 3 pounds each.
Due to elevated levels of hCG, people carrying multiples may experience more nausea and vomiting than those carrying only one baby, explains Dr. Greves. Hyperemesis gravidarum, a condition that's often compared to morning sickness (but is infinitely more severe), is also more likely with a multiple pregnancy.
Movement from your babies might feel like gas or “fluttering” at first. The round ligaments that support your uterus (and connects the front part of your uterus to your groin) is being stretched as your uterus grows quickly. This may cause sharp pain when you move.
When more than one ovum is fertilized and implants in the uterus, the result is dizygotic (fraternal) twins, triplets, or other multiples. Although two fetuses develop simultaneously in superfetation, they differ in maturity, having been conceived days or even weeks apart.
Monoamniotic-monochorionic Twins
These types of twins share a chorion, placenta, and an amniotic sac. This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.