Twin pregnancy

Twin pregnancy account for approximately 3% of live births in the United States. In the absence of assisted reproductive technology, dizygotic twins (when two eggs are fertilized by two separate sperm) are far more common than monozygotic twins (created with one egg and one sperm or one zygote which then splits into two) and account for 70% of all twin pregnancies ¹. Whereas the instance of dizygotic twins (fraternal twins) is variable in different populations, the prevalence of monozygotic twinning is globally constant at 3 to 5 per a thousand births. Except for post-term pregnancy and fetal macrosomia, pregnancy-related risks are increased. Preterm birth is a prominent risk associated with twin pregnancy with others at risk for fetal growth restriction, congenital anomalies, and abnormal placentation. Other obstetric risks that increase with twin pregnancy include the risk of preeclampsia and gestational diabetes.

Most twin or multiple pregnancies are discovered during an ultrasound. During this exam, sound waves are used to create images of your uterus and baby or babies.

The normal length of gestation (period of time spent developing in the womb) for a single baby is around 40 weeks. However, gestation for twins, either identical or fraternal, is usually around 38 weeks. This shorter time is due to the increased demands on the mother’s body, and the inability of the babies to receive all the nutrients they need in the womb.

As twins are usually premature, they are more likely to have lower birthweights. Prematurity is associated with increased risk of a number of disorders, including jaundice.

Because a twin pregnancy can be more complicated than a single pregnancy, health professionals usually recommend specialist antenatal care, rather than shared care or midwife-only care. If you have any complications, specialist checks can pick them up early, which means they can be treated early.

You might be advised to see an obstetrician. Obstetricians are skilled and experienced in providing antenatal care for twin pregnancies.

Also, health professionals will usually recommend that you give birth in a hospital, rather than in a birth center or at home. Hospitals have the facilities needed to manage any complications of a twin pregnancy, like premature birth.

Some people think that if you are pregnant with twins, you need a lot of extra food. Whereas single-born pregnancies require 300 extra calories a day, most experts agree that twin pregnancies need around 1,000 extra calories a day. The type of food you eat is more important for your babies than how much you eat. Talk to your midwife or doctor about the best diet for you. You might also be advised to take certain supplements, such as folate and iron supplements.

Morning sickness or in most women’s cases, all-day sickness can be eased by eating small snacks frequently. Keeping a little something in your stomach at all times can help take the edge off of the nausea. Low-fat yogurt, fruit, smoothies, crackers, and protein shakes are all good snack options.

In addition to the extra calories, it is important to sip on water throughout the day. Keeping well hydrated may drive you crazy in later months when it seems like you’re running to the bathroom every 5 minutes; however, your babies’ extra blood flow and removal of wastes depends on it. It may help to drink more water earlier in the day and then stop after 8:00 pm so that you can sleep longer stretches at night between bathroom breaks.

Having a healthy lifestyle and diet during pregnancy is important. Eat well, take gentle exercise, drink lots of fluid and, if you feel stressed, ask for support from friends and family, or talk to your midwife or doctor.

Make sure you look after yourself. Being pregnant with twins can be more tiring both physically and emotionally. All of the common pregnancy discomforts are likely to be more noticeable with twins.

Mothers of multiple births also face higher rates of postpartum depression. Talk to your doctor or other health professional if you feel you may be experiencing this.

What does having twin pregnancy or multiple pregnancy mean for you?

Taking care of yourself is the best way to take care of your babies. If you’re carrying multiples, you can expect:

• More-frequent checkups. You’ll see your health care provider often to track your babies’ growth and development, monitor your health, and watch for signs of preterm labor. You might need frequent ultrasounds or other tests, especially as your pregnancy progresses.
• More weight gain. Gaining the right amount of weight can support your babies’ health. For twins, the recommendation is typically 37 to 54 pounds (about 17 to 25 kilograms) for women who have a normal weight before pregnancy. This can typically be accomplished by eating an extra 600 calories a day. Work with your health care provider to determine what’s right for you.
• Earlier delivery. If labor doesn’t start on its own first, your health care provider might recommend labor induction or a C-section at a certain point in your third trimester to decrease the risk of complications in the third trimester.

Will your twins be born early?

Health professionals usually aim for twins to be born at 37-38 weeks unless problems develop earlier or there’s a good reason to delay birth.

About 60% of twins are born before 37 weeks, while single babies are born at around 40 weeks.

If you know your twins will be born early, you can get ready for premature birth.

What are identical twins?

Twins conceived from one egg and one sperm are called identical or ‘monozygotic’ (one-cell) twins. Identical twins occur when the fertilized egg divides in two while it is still a tiny collection of cells. The self-contained halves then develop into two babies, with exactly the same genetic information. Around one in three sets of twins is identical. What causes the fertilized egg to split in two remains a mystery.

Types of identical twins

Depending on when the fertilized egg divides in two, monozygotic twins may:

• each have their own placenta, inner membrane (amnion) and outer membrane (chorion)
• share one placenta and one outer membrane, but have two inner membranes
• share one placenta, one outer membrane and one inner membrane.

If the division of the fertilized egg is incomplete, the twins will be conjoined (previously known as ‘Siamese’ twins).

Approximately one-quarter of identical twins are mirror images of each other, which means the right side of one child matches the left side of their twin. It is not known what causes this.

Twin pregnancy causes

Sometimes a twin or triplet pregnancy just happens. In other cases, specific factors are at play. For example, a twin pregnancy is more likely as you get older because hormonal changes can cause more than one egg to be released at a time. Use of assisted reproductive technologies — such as in vitro fertilization (IVF) also increases the odds of twins or other multiples.

Multiple births are more common than they used to be, due to the increased use of assisted reproductive techniques, in particular the use of fertility drugs. Older women are more likely to have a multiple pregnancy and, because the average age at which women give birth is rising, this is also a contributing factor. Twins account for more than 90 per cent of multiple births. There are two types of twins – identical (monozygotic) and fraternal (dizygotic).

1. Fraternal twins or dizygotic twins is the most common kind of twins — occur when two separate eggs are fertilized by two different sperm and produce two genetically unique children, who are no more alike than individual siblings born at different times. Each twin has his or her own placenta and amniotic sac (inner membrane and outer membrane). The twins can be two girls, two boys, or a boy and a girl. Contrary to popular belief, the incidence of twins does not skip generations. Twins are equally likely to be female or male.
2. Identical twins or monozygotic twins occur when a single fertilized egg splits and develops into two babies with exactly the same genetic information. Identical twins might share a placenta and an amniotic sac or the twins might share a placenta and each have separate amniotic sacs. Genetically, the two babies are identical. They’ll be the same sex and share physical traits and characteristics. Rarely, identical twins fail to completely separate into two individuals. These babies are known as conjoined twins.

Triplets and other higher order multiples can be identical, fraternal or a combination of both. Triplets or more require a closely monitored pregnancy.

Factors that increases the likelihood of having twins

Some women are more likely than others to give birth to twins. The factors that increase the likelihood include the following:

• Age of the mother – women in their 30s and 40s have higher levels of the sex hormone estrogen than younger women, which means that their ovaries are stimulated to produce more than one egg at a time
• Number of previous pregnancies – the greater the number of pregnancies a woman has already had, the higher her likelihood of conceiving twins
• Heredity – a woman is more likely to conceive fraternal twins if she is a fraternal twin, has already had fraternal twins, or has siblings who are fraternal twins
• Race – black African women have the highest incidence of twins, while Asian women have the lowest
• Assisted reproductive techniques (ART)– many procedures rely on stimulating the ovaries with fertility drugs to produce eggs, which can result in several eggs being released per ovulation
• In vitro fertilization (IVF) – multiple embryos are often transferred to the woman’s uterus to increase the chance of success.

Twin pregnancy signs and symptoms

Many women who are expecting twins find that they have quite noticeable and very early pregnancy symptoms, including tiredness, emotional ups and downs, nausea, vomiting and constipation.

Also, body changes with a twin pregnancy are much more obvious than with a single pregnancy. If you’re pregnant with twins, you might gain 16-20 kg (compared to 10-15 kg with a single pregnancy). Unfortunately, stretch marks, bloating, varicose veins and hemorrhoids are all more common in a twin pregnancy. These changes might affect the way you feel about your body.

You can talk with your doctor or midwife about the changes in your body and how you feel about these changes.

Sacroiliac joint dysfunction is a common involvement in twin gestations and prophylactic spine strengthening exercises in early second trimester can be helpful.

Because twins have an increased chance of being born early, any symptoms or concerns must be addressed for the safety of your babies. Bleeding or vaginal discharge, contractions that are becoming more frequent, pressure in the pelvis or lower back, or even diarrhea can all be signs of preterm labor. And while early bleeding in the first trimester could be the normal phenomenon of the twins implanting in the uterine wall, you should call your obstetrician if you experience bleeding at any point.

Twin pregnancies can also increase the chances of preeclampsia, a condition in which the mother has increased blood pressure, protein in the urine (detectable by urinalysis), and more swelling than is normal in pregnancy. If you notice rapid weight gain or headaches, alert your obstetrician so you may be examined as soon as possible. Depending on the severity of the situation, treatment may range from bed rest, to hospital-administered medications, to immediate delivery of the babies (the only “cure” for preeclampsia).

Twin pregnancy potential complications

Twin pregnancies are associated with more frequent complications for both the mother and the babies. However, healthy twin pregnancies and multiple pregnancies are born every day. Still, it’s important to be aware of possible complications. For example:

• Women with twin pregnancies are more likely to have pregnancy health problems and complications like severe morning sickness that is persistent, gestational diabetes, pre-eclampsia, premature labor due to waters breaking prematurely giving rise to preterm delivery of babies and bleeding.
• Gestational diabetes. If you’re carrying multiples, you’re at increased risk of gestational diabetes. This condition causes high blood sugar that can affect your pregnancy and your babies’ health. An endocrinologist, a registered dietitian or a diabetes educator can help you learn to manage your blood sugar level during your pregnancy.
• High blood pressure (pre-eclampsia). If you’re carrying multiples, you’re at increased risk of developing high blood pressure disorders during pregnancy.
• Twin-twin transfusion. Twins who share a placenta might have extra complications. Sometimes their blood supply is shared unequally, which can cause health problems for both twins. Or if the placenta itself is shared unequally, this can mean that one twin doesn’t get enough nutrients and doesn’t grow as well. This is a serious complication for both babies that might result in heart complications and the need for fetal procedures while you’re still pregnant.
• Premature birth. The more babies you’re carrying, the less likely you are to carry your pregnancy to term. If you have signs of preterm labor, you might be given injections of a steroid medication to speed your babies’ lung development. Even then, your baby might experience complications, including breathing and digestive difficulties, vision problems, and infection. Interventions to prolong pregnancy, such as bedrest, aren’t recommended because they haven’t been proved to decrease disease and death in newborns.
• C-section delivery. For twins, vaginal delivery is often possible if the first baby is in a head-down position. If not, a C-section might be recommended. In some cases, complications after the vaginal delivery of the first twin might require a C-section delivery for the second twin. For higher order multiples, the more common route of delivery is a C-section.
• Miscarriage
• Vanishing twin syndrome — a twin that is seen on ultrasound early but disappears by the next ultrasound.
• Hemorrhage (bleeding) around the birth
• Complications during labor
• Low birth weight

You can’t stop some of these complications from happening. But you can reduce your risk of having them or stop them from getting worse – by going to your antenatal appointments and telling your obstetrician, doctor or midwife if you have any physical symptoms or you feel that something is wrong.

Twin pregnancy diagnosis

The only definite way to find out whether you’re having twins or other multiples is to have an ultrasound scan. You can’t rely on hormone tests to find out whether you’re pregnant with twins.

The best time to have this ultrasound is at 10-12 weeks of pregnancy. This is usually when your health professional can say for sure how many fetuses, placentas and amniotic sacs there are. This information can tell you whether you have identical or fraternal twins. And the information also helps your health professionals recommend the right pregnancy care for you.

It is important to know whether your twins are sharing a placenta, as sharing a placenta also means sharing the blood supply from the mother. If the sharing of the blood supply is unequal, this can lead to complications. For this reason, women carrying twins sharing a placenta will need to have more frequent antenatal check-ups.

Twins sharing an inner membrane (which means they share the amniotic sac) carry an even higher risk of complications, as there is the potential for their umbilical cords to become tangled and to cut off their blood supply. In this case the pregnancy is monitored even more closely, and it may be recommended that your twins be delivered earlier.

Sometimes a seemingly normal twin pregnancy is later found to have only one baby. This is known as vanishing twin syndrome. Such an episode can be heartbreaking, frustrating and confusing. Often, there’s no clear explanation for the loss.

Zygosity testing

It is difficult to tell if twins are identical or fraternal at birth. Fraternal twins are born with individual sets of membranes, but some identical twins can also be.

One way to tell the difference is to have the twins DNA-tested this is also known as zygosity testing. Identical twins share the same genetic information, while fraternal twins share around half.

DNA testing can be done with a sample of cheek cells, collected painlessly, or by performing blood group examinations, which require a blood sample to be taken.

While the distinction may not seem important if you have two (or more) healthy babies, it can be useful to know for health reasons because identical twins have a high likelihood of experiencing the same illnesses or having the same health condition. Identical twins are also compatible for organ transplantation, should it be required.

Twin pregnancy treatment

If you’re pregnant with twins, you’ll need a higher level of care, which means more frequent antenatal appointments and tests during your pregnancy. Routine obstetric care includes review every 4 weeks until 24 weeks and after that every 2 weeks until 32 weeks when weekly evaluations occur. Antenatal appointments are a good chance to get health and lifestyle support if you need it. You can also get information about pregnancy, labor, birth and early parenting. You probably won’t need lots of extra blood tests, but you will need more ultrasounds.

If you have twins with separate placentas, it’s generally recommended that you have ultrasounds at 12-13 weeks, 20 weeks, and then every four weeks until your babies are born. You might have more frequent ultrasounds than this.

A twin pregnancy with babies sharing one placenta might be more complicated, so it’s generally recommended that you have ultrasounds about every two weeks from 12 weeks.

Twin gestations typically concluded around 36 weeks of gestation. Elective delivery in dizygotic twin gestation that is addressed and without any complications can be deferred to the 38 to 39-week obstetric window. Monochorionic diamniotic twin gestations are best managed expectantly until her to 34 weeks, and after that, delivery becomes an option should significant complications established. Typically elective delivery is deferred to the 36 to 37-week window as long as the obstetric course is entirely stable. The mode of delivery depends on prior obstetric history, current obstetric history, as well as fetal presentation. Vaginal delivery is entirely permissible and indeed recommended cephalic-cephalic presentations and may be considered for cephalic-nonspecific presentations. Breech presentation suppressed delivery device elective cesarean section. Intrapartum obstetric care includes surveillance for dysfunctional labor and risk for postpartum hemorrhage. In event of prematurity, appropriate neonatal care should be arranged.

Unique treatment options for complications of monochorionic dichorionic gestation may be necessary such as laser photoablation of the vascular connections when twin-twin transfusion syndrome occurs ². In such scenarios, fetal echocardiography is also warranted to exclude acquired pulmonary stenosis in the donor twin. The occurrence of hydrops fetalis represents an advanced age for twin-twin transfusion syndrome, and as definitive fetal treatment is not available after 26 weeks, delivery may represent the best obstetric intervention. In the context of monochorionic diamniotic twin gestation, the demise of a single fetus places the surviving fetus at risk of acute hypotension and resultant 10% to 15% risk for death. Surviving fetuses may bear stigmata of visceral ischemic injury that may include porencephalic brain cysts or disruption anterior abdominal wall. When a fetal demise occurs, in addition to obstetric challenges, there are additional emotional challenges for the couple, and they deserve supportive care. Fetal treatments are best deferred to tertiary centers. More unusual fetal treatments may include photocoagulation of the umbilical cord to optimize chances for survival of a single fetus when the survival of both the fetuses is not an achievable obstetric goal (such as twin reversed arterial perfusion). In monochorionic monoamniotic twin gestations, severing of the occluded cord may be preferred if cord entanglement is present.

Healthy eating

Healthy eating in pregnancy is about a healthy, well-balanced diet, full of vitamins and minerals.

When you’re pregnant with twins, your doctor or midwife might recommend that you get expert advice about your dietary intake of protein, carbohydrates, folate, iron, calcium, iodine, fats and overall nutrients. Dietitians have qualifications and skills to give you expert nutrition and dietary advice.

Vaginal or caesarean birth

It’s good to talk with your obstetrician and midwife about your health and your babies’ health and whether vaginal or caesarean birth will be better for you and your twins.

If you’re having twins, you’re almost twice as likely to have a caesarean birth.

You can discuss with your obstetrician the most appropriate time and ‘way’ for you to give birth to your twins.

Caring for twins

Healthy multiples have the same needs as other newborns. But you might need more rest and support than you imagined, especially if your babies are born prematurely or need special medical care after birth. You’re also at higher risk of postpartum depression. If you experience any symptoms of postpartum depression, talk to your doctor.

Take time to enjoy your babies — and ask friends, loved ones and others for help when you need it.

References

1. Gill P, Lende MN, Van Hook MD JW. Twin Births. [Updated 2019 May 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK493200
2. Bautista TN, Krebs TL, Jnah A, Newberry D. Twin-to-Twin Transfusion Syndrome: A Case Report. Neonatal Netw. 2018 Sep;37(5):292-302.