The progress of reproductive technologies and in vitro fertilization has played a major role in this increase. As we speak about history, the vast majority of multiple pregnancies that occurred in the past were diagnosed during the intrapartum period [ 2 ]. Today, as the use of ultrasound has become a routine in daily medical practice, multiple pregnancies are diagnosed in the initial ultrasound scan [ 3 ]. Beyond the diagnosis of early multiple pregnancy, ultrasound scan is more than necessary to define chorionicity, amnionicity, and gestational age [ 4 ].
In this chapter, we will present the ultrasound figures that help us determine gestational age, chorionicity, and amnionicity, focused on the 14 first weeks of gestation in multiple pregnancies.
Nonetheless, we will review some cases from the literature that show that situations can be a little more complicated and may lead to a false diagnosis of chorionicity and amnionicity, in order to highlight that when we manage multiple pregnancies, we have to be alert about exceptions despite being infrequent [ 5 ].
A twin pregnancy can be either dizygotic two-third of twin pregnancies , in which two different eggs are fertilized by two different sperms, and in this case, the pregnancy is always dichorionic-diamniotic or monozygotic. A monozygotic pregnancy occurs when an egg is fertilized by one sperm, producing one embryo, which can split any time, more commonly between day 2 and day 13 after fertilization.
Chorionicity and amnionicity are differentiated by the timing of embryo splitting. Table 1 presents this differentiation and the frequency of each type of a monozygotic pregnancy [ 3 ]. How the chorionicity and amnionicity are differentiated by the timing of the embryo splitting in monozygotic twins Table is modified from Simpson L, [ 6 ].
The accurate determination of gestational age is critical for pregnancy management as it shows wherever the measurements of the fetus are in line for the estimate gestational age [ 4 ]. In addition, a correct pregnancy dating is necessary not only for the appropriate timing for screening and diagnostic testing but also for optimal scheduling of delivery [ 6 ]. For women with regular cycles, the date of the last menstrual period is used to estimate gestational age, taking into account the biological variability and correct the cycle length.
For IVF pregnancies, the date of the embryo transfer has been used to define pregnancy dating. The vast majority of authors embraced with multiple pregnancies agree that during the second trimester the evaluation of gestational age is more accurate and it is statistically superior to the second trimester [ 4 ].
Moreover, there is an agreement that the parameters and formulas that have been used for dating singleton pregnancies are also accurate for dating multiple pregnancies, since studies in this area include a combination of singleton and multiple pregnancies [ 7 , 8 , 9 ]. In the first trimester—before the 14th week of gestation—crown-rump length CRL is the parameter that is used in order to estimate gestational age with 5—7 days of deviation [ 7 , 8 , 9 ].
If there is a doubt about the reliability of the menstrual cycle or if the woman is administrated late for care, a repeat scan in 3—4 weeks can be helpful to determine pregnancy dating [ 10 ].
Modest size discordance is very common in multiple pregnancies [ 4 ]. Some studies suggest that pregnancy dating must be defined by using the mean of the fetuses [ 11 ]. However, more recent studies agreed that if the gestational age is based on the CRL of the larger twin, the possibility of missing a fetus that might develop intrauterine fetal growth restriction IUGR is decreased [ 12 ].
Salomon et al. In the second trimester, a combination of parameters is used to define pregnancy dating such as abdominal circumference, femur length, and biparietal diameter [ 8 ]. Further discussion about calculating gestational age in second trimester is beyond the scope of this chapter. Early and accurate definition of chorionicity and amnionicity has an undeniably determinant role in the management of multiple pregnancies, since chorionicity plays a key role in the appearance of complications: monochorionic-monoamniotic twins present the highest mortality and morbidity.
There is no doubt that the continuous surveillance and the timely intervention can optimize the outcome of the pregnancy [ 4 ]. The determination of chorionicity and amnionicity is better to be done in the first trimester [ 4 ]. At this point, we will classify the determination based on gestational age, separated in two periods: the first before the 10th week of gestation and the second that includes the period from week 10 to week Three ultrasound findings can help in the detection of chorionicity: These are 1 the number of observable gestational sacs, 2 the number of amniotic sacs within the chorionic cavity, and 3 the number of yolk sacs [ 4 ].
The number of the gestational sacs and the number of fetal heartbeats in early multiple pregnancy scan are strongly related with chorionicity: each gestational sac will form a distinct placenta and chorion. Therefore, visualization of a single gestational sac with two visible heart beats indicates a monochorionic twin pregnancy, while the presentation of two distinctive gestational sacs implies a dichorionic pregnancy Picture 1 [ 18 ].
Dichorionic diamniotic pregnancy at 5 weeks of gestation. The two separate gestational sacs with one yolk sac each are visible and a thick septum separates them. Identification of the number of amniotic sacs present in a single gestational sac helps define amnionicity in a monochorionic pregnancy. Prior to the 10th week of gestation, the amnions grow outward from the embryonic disk and at that age are not big enough to contact each other and create the intertwin septum [ 4 ].
As a result, separate and distinct amnions indicate a diamniotic twin pregnancy Pictures 2a , b and 3a , b. The evaluation of the amnion should be done diligently via transvaginal ultrasound since the intertwin membrane is extremely thin and it may be invisible via transabdominal ultrasound.
Even when the separate amnions cannot be visualized via the transvaginal ultrasound, their absence can be confirmed by demonstrating umbilical cord enlargement by using pulsed wave Doppler and identifying two distinct heart rates [ 3 ]. In addition, the impossible visualization of the intertwin membrane may be technical: if the membrane is parallel to the ultrasound beam or because the ultrasound gain is low, the membrane may be hard to evaluate.
This finding is true of both fresh and frozen embryo transfer cycles. This pregnancy advantage is not seen in young patients and in patients using donor egg, and single embryo transfer maximizes birth outcomes. Early pregnancy loss is unfortunately a common clinical event.
This number can be two to four fold greater if unrecognized early miscarriages are included. In spontaneous conceptions, miscarriage is more common with multiple pregnancy.
For many decades it has been suggested that twins are more often conceived than born [ 3 ]. More than thirty years later, other studies confirmed his hypothesis: three times more twins were identified among aborted pregnancies than term pregnancies [ 4 , 5 ]. The true prevalence of multiple pregnancy sacs or multiple fetal heartbeats in early pregnancies is not known due to undercounting [ 6 ] and vanishing twins [ 7 , 8 ].
However, in vitro fertilization IVF studies show lower rates of miscarriage with twin gestations than singletons [ 9 — 11 ]. This is true for total pregnancy loss loss of all sacs and fetal heart beats as well as for pregnancy loss per gestational sac in multiple pregnancies when compared to singletons [ 9 ].
Due to earlier and closer clinical follow up of artificial reproductive technology ART pregnancies, more multiple gestational sacs and heartbeats are likely recognized in these women than in spontaneous conceptions from fertile women. Pregnancy loss is known to occur for embryonic and maternal factors, but many times no answer is found.
Aneuploidy likely accounts for a significant amount [ 12 ]. Relatively little is understood about the rate of pregnancy loss among fresh and frozen embryos since miscarriages still occur in women with a normal uterine cavity and with known euploid embryos.
This constrains physician counselling regarding the number of embryos to transfer. In addition to managing patient expectations with regards to achieving a positive pregnancy test, it is equally important to counsel patients on pregnancy outcomes once they achieve their initial positive pregnancy test.
In the current study, we aim to quantify the chance of live birth and intermediate pregnancy outcomes in women with an initial positive pregnancy test and determine if this outcome differs between fresh IVF and frozen embryo transfer FET cycles.
Additionally, we investigate the relationship between multiple pregnancy and pregnancy loss in both fresh and frozen cycles. We performed a retrospective local cohort study of all consecutive patients undergoing IVF in a single, private center at Island Reproductive Services, Staten Island, NY, between January 1st, and December 31st, Cycles were excluded if they did not result in embryo transfer either purposefully for embryo banking, if transfer was cancelled for overstimulation, or if no embryos were available for transfer.
Donor cycles were included. More than one cycle per patient was included if applicable. Biochemical pregnancy was defined by the presence of a positive serum hCG, with or without an intrauterine gestational sac seen on transvaginal sonogram, but without fetal heartbeat.
Implantation rate was defined as the number of fetal heartbeats per embryo transferred. Total pregnancy loss SAB was defined as the loss of all fetal heart beats previously identified.
Pregnancy was defined by a positive hCG drawn 14 days after fresh egg retrieval or at the equivalent time frame after FET. Partial pregnancy loss PSAB was defined as a pregnancy with more than 1 sac seen on ultrasound independent of the presence of cardiac activity and a loss of one or more sacs but with the end result still being a live birth.
Data regarding patient characteristics age, BMI, maximum FSH , IVF cycle parameters estradiol levels, number of eggs retrieved, and endometrial thickness and pregnancy outcomes hCG level, number of sacs, clinical pregnancy, implantation rate, partial and total miscarriage rates, and live birth were collected. T -test and Chi-square test were used to analyze patient and pregnancy data with linear and logistic regression when appropriate.
Most patients were young age Among fresh IVF cycles, transfers took place at the blastocyst stage and at the cleavage stage. Among FET cycles, were blastocyst transfers and were cleavage stage transfers. As expected, peak estradiol levels were higher with fresh cycles, and endometrial thickness was slightly higher as well Table 1. Slightly more embryos were transferred in fresh cycles.
Other patient characteristics did not differ between cycle types Table 1. On average, patients froze 3. Overall, pregnancy outcome data were similar between fresh and frozen cycles. Clinical pregnancy, implantation and live birth rates did not differ. Biochemical pregnancies were slightly more common for frozen cycles Table 1. When analyzing pregnancy outcomes by SART reporting age groups, comparable outcomes were seen for clinical pregnancy, live birth, implantation rate, and SAB by cycle type Figure 1.
Overall, for every additional embryo transferred, the risk of multiple pregnancy rose OR 1. This was even more significant for patients under age 35 OR 1. Medical professionals use ultrasound to work out how many placentas twins have. The earlier the ultrasound, the more accurately it can say how many placentas there are. It gets harder to work out later in pregnancy.
After the birth, the placentas should be looked at to confirm or determine what type of twins they are. Same-sex twins with separate placentas can be fraternal or identical.
To find out whether twins are identical or fraternal, you can ask for a genetic test after your babies are born. This is called a zygosity test. Identical twins are more likely than fraternal twins to get the same illness. If one of a pair of identical twins is diagnosed with a particular disease or health condition, like high blood pressure, the other twin should be checked often for early symptoms.
Because of their genetic make-up, identical twins will always be compatible for organ transplantation , if they ever need it. Fraternal twins are compatible only sometimes. Some identical twins are mirror twins — for example, their hair parts on opposite sides, they are oppositely handed, or they have birthmarks on opposite sides of their body.
In some rare cases, their internal organs can be mirror images of each other. In very rare cases, twins can be born physically joined together in different ways. A Guide for Patients. Multiple births are much more common today than they were in the past.
There are more multiple births today in part because more women are receiving infertility treatment, which carries a risk of multiple pregnancy. Also, more women are waiting until later in life to attempt pregnancy, and older women are more likely than younger women to get pregnant with multiples, especially with fertility treatment. Although major medical advances have improved the outcomes of multiple births, multiple births still are associated with significant medical risks and complications for the mother and children.
If you are at risk for a multiple pregnancy, this booklet will help you learn how and why multiple pregnancies occur and the unique issues associated with carrying and delivering a multiple pregnancy.
You may know someone who has twins, but do you know how twins occur and how they develop? There are two types of twins: identical and fraternal non-identical. Identical twins occur when a single embryo, created by the union of a sperm and an egg, divides into two embryos. Each embryo is monozygotic, genetically identical, and both will be the same sex. Depending on when the division occurs, identical twins may have separate placentas and gestational sacs, or they may share a single placenta but have separate sacs.
In rare cases, identical twins may be in the same amniotic sac. Non-identical twins occur when two separate eggs are each fertilized by a separate sperm. The two embryos that result are dizygotic, not genetically identical, and can be the same or different sex. Most of the time, this is the type of twinning that occurs from assisted reproduction procedures.
Spontaneous losses are even higher in triplet and quadruplet pregnancies. When a fetus is lost in the first trimester, the remaining fetus or fetuses generally continue to develop normally, although vaginal bleeding may occur. Ultrasound examinations performed early in the 5th week of pregnancy occasionally may fail to identify all fetuses.
After 6 to 8 weeks, ultrasound should provide an accurate assessment of the number of fetuses. Naturally, twins occur in about one in pregnancies, triplets in about one in 10, pregnancies, and quadruplets in about one in , pregnancies. The main factor that increases your chances of having a multiple pregnancy is the use of infertility treatment, but there are other factors.
Your race, age, heredity, or history of prior pregnancy does not increase your chance of having identical twins but does increase your chance of having fraternal twins. Infertility treatment increases your risk of having twins, both identical and fraternal.
The overall rate of twins for all races in the United Statees is around 33 per 1, live births. Black and non-Hispanic white women have similar rates of twinning, while Hispanic women are less likely. Non-identical twin women give birth to twins at the rate of 1 set per 60 births.
However, non-identical male twins father twins at a rate of 1 set per births. Maternal age and prior pregnancy history. The frequency of twins increases with maternal age and number of pregnancies. Women between 35 to 40 years of age with 4 or more children are 3 times more likely to have twins than a woman under 20 without children.
Maternal height and weight. Non-identical twins are more common in large and tall women than in small women. This may be related more to nutrition than to body size alone. During World War II, the incidence of non-identical twinning decreased in Europe when food was not readily available. Fertility Drugs and Assisted Reproductive Technology. Multiple pregnancy is more common in women who utilize fertility medications to undergo ovulation induction or superovulation.
Use of drugs to cause superovulation has caused the vast majority of the increase in the multiples. Assisted reproductive technology ART procedures such as in vitro fertilization IVF also contribute to the increase in the multiple birth rate. The risk of multiple pregnancy increases as the number of embryos transferred increases. The duration of a normal singleton pregnancy ranges from 37 weeks to 42 weeks from the time of the last menstrual period. Twin pregnancies occasionally progress to 40 weeks but almost always deliver early.
As the number of fetuses increases, the expected duration of the pregnancy decreases. The average duration is 35 weeks for twins, 33 weeks for triplets, and 30 weeks for quadruplets. Complications increase with each additional fetus in a multiple pregnancy and include many medical issues that will be discussed below.
In addition to these, there is a higher incidence of severe nausea and vomiting, cesarean section, or forceps delivery. If you are pregnant with twins or more, or if you are at risk for a multiple pregnancy, you should be aware of these and other potential problems you might experience. Preterm labor and birth pose the greatest risk to a multiple pregnancy. Cesarean section is often needed for twin pregnancies and is expected for delivery of triplets.
Since preterm labor and birth present such serious risks, the pregnant mother must understand the warning signs of early labor.
Sometimes, preterm delivery can be delayed by a few days or more if it is detected early. Each day gained provides valuable fetal growth and development. Once a woman is in advanced labor, delivery cannot be stopped. In rare instances, delivery of a second twin can be delayed.
This delay, when possible, allows for continued growth in the protective environment of the uterus. Currently, there are no effective treatments to prevent preterm birth of multiples.
The placenta is attached to the wall of the uterus, and the fetus is attached to the placenta by the umbilical cord.
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