Human chorionic gonadotropin rise in normal and vanishing twin pregnancies

β-Human Chorionic Gonadotropin Dynamics in Early Gestational Events: A Practical and Updated Reappraisal

In the last decade, the widespread use of transvaginal ultrasound and the availability of highly specific serum assays of human chorionic gonadotropin (hCG) have become mainstays in the evaluation of early pregnancy. These tests have revolutionized the management of pregnancies of unknown location and markedly reduced the morbidity and mortality associated with the misdiagnosis of ectopic pregnancy. However, despite several advances, their misuse and misinterpretations are still common, leading to an increased use of healthcare resources, patient misinformation, and anxiety. This narrative review aims to succinctly summarize the β-hCG dynamics in early gestation and provide general gynecologists a practical approach to patients with first-trimester symptomatic pregnancy.

Timing of the luteal-placental shift is delayed with additional fetuses in litter-bearing callitrichid monkeys, Saguinus oedipus and Callithrix jacchus

The luteal-placental shift is an important milestone of mammalian pregnancy signifying when endocrine control of pregnancy shifts from the corpus luteum of the ovary to the placenta. The corpus luteum is maintained by chorionic gonadotropin (CG). Upon sufficient placental maturation, CG production wanes, the corpus luteum involutes, and control is shifted to the placenta, one consequence of which is a midgestational rise in glucocorticoid production, especially cortisol and cortisone, by both mother and fetus. Glucocorticoids are involved in initiating parturition, prenatal programming of offspring phenotype, and maturing fetal organs. Limited evidence from human pregnancy suggests that the timing of this shift is delayed in twin pregnancies, but little is known about the timing of the luteal-placental shift in litter-bearing monkeys from the primate family Callitrichidae. Here we provide evidence from cotton-top tamarins (Saguinus oedipus) and common marmosets (Callithrix jacchus) of longer duration of elevated CG associated with multiple infant births compared to single births. Urinary profiles from cotton-top tamarins demonstrate that the decline of the extended elevation of CG precedes the onset of the midpregnancy sustained rise in glucocorticoids; this shift occurs later with an increase from one to two fetuses carried to term. In the common marmoset, the onset of the sustained rise of glucocorticoids in maternal urine is also delayed with an increase in infant number. Total urinary glucocorticoid levels during the last half of gestation increase monthly but do not differ by infant number. The significant delay in the luteal-placental shift suggests a longer period of placental maturation is needed to support a greater number of fetuses.

The vanishing twin: Diagnosis and implications

Vanishing twin syndrome (VTS), defined by first-trimester spontaneous loss of a twin, is a common phenomenon with a reported prevalence of 15-35% of twin pregnancies. The etiology of VTS is obscure. Still, several risk factors have been identified, including an increased number of embryos transferred in pregnancies conceived by in vitro fertilization, an initial increased number of gestational sacs and advanced maternal age. The effect of VTS on obstetric and perinatal outcomes is controversial. Several studies have reported that pregnancies with VTS were associated with increased risk for preterm birth and small for gestational age neonates compared to singleton pregnancies, while others showed no difference in perinatal outcomes. The prevalence of placental vascular and anatomic abnormalities such as small placentas was higher in VTS. These findings lay an essential foundation for understanding how this phenomenon affects obstetric and perinatal outcomes of the surviving pregnancy.

Temporal persistence of residual fetal cell-free DNA from a deceased cotwin after selective fetal reduction in dichorionic diamniotic twin pregnancies

OBJECTIVES

To determine the temporal persistence of the residual cell-free DNA (cfDNA) of the deceased cotwin in maternal circulation after selective fetal reduction and evaluate its long persistence in noninvasive prenatal testing (NIPT).

METHODS

Dichorionic diamniotic twins (N = 5) undergoing selective fetal reduction because of a trisomy were recruited. After informed consent, maternal blood was collected immediately before reduction and periodically after reduction until birth. The plasma cfDNA of each sample was sequenced and analyzed for fetal aneuploidy and fetal fractions.

RESULTS

In all pregnancies, the fetal fraction of the cfDNA of the deceased fetus increased to peak at 7-9 weeks after fetal reduction, and subsequently decreased gradually to almost undetectable during the late third trimester. The NIPT T-scores persistently reflected the detection of fetal trisomy up to 16 (median 9.5) weeks after fetal reduction.

CONCLUSIONS

Residual cfDNA from the deceased cotwin after selective reduction at 14-17 gestational weeks led to the persistent generation of false-positive NIPT results for up to 16 weeks postdemise. Thus, providing NIPT for pregnancies with a cotwin demise in early second trimester is prone to misleading results and not recommended.

Can early β-human chorionic gonadotropin predict birth of singletons and twins after in vitro fertilization?

OBJECTIVE

To assess the predictive value for clinical pregnancy outcome of β-hCG level at 13 d after embryo transfer.

METHODS

Retrospective study of IVF clinical pregnancies diagnosed at 6 weeks. We calculated the value of β-hCG level at 13 d after embryo transfer to predict live births.

RESULTS

We analyzed 177 IVF cycles between 2009 and 2014 (50 singleton births, 50 twin births, 27 sets with a vanishing twin, 43 first trimester singleton pregnancy loss and seven first trimester total twin pregnancy loss). Singleton pregnancies with a β-hCG concentration <85 mIU/mL had an 89% risk of having a first trimester loss whereas a concentration >386 mU/mL had a 91% chance of a live birth. Twin pregnancies with a concentration <207 mIU/mL had only a 33% chance of delivering twins and a 55% risk of having a vanishing twin; whereas a level >768 mIU/mL was associated with a 81% chance of live twin birth and a low risk (19%) of having a vanishing twin. Age, type and duration of infertility, body mass index (BMI) and number of fertilized oocytes did not affect these calculations.

CONCLUSIONS

β-hCG level at 13 d after embryo transfer might predict outcomes in clinical singleton and twin pregnancies following IVF.

Detection of triploid, molar, and vanishing twin pregnancies by a single-nucleotide polymorphism-based noninvasive prenatal test

OBJECTIVE

We sought to determine the ability of single-nucleotide polymorphism-based noninvasive prenatal testing (NIPT) to identify triploid, unrecognized twin, and vanishing twin pregnancies.

STUDY DESIGN

The study included 30,795 consecutive reported clinical cases received for NIPT for fetal whole-chromosome aneuploidies; known multiple gestations were excluded. Cell-free DNA was isolated from maternal blood samples, amplified via 19,488-plex polymerase chain reaction, and sequenced. Sequencing results were analyzed to determine fetal chromosome copy number and to identify the presence of additional fetal haplotypes.

RESULTS

Additional fetal haplotypes, indicative of fetal triploidy, vanishing twin, or undetected twin pregnancy, were identified in 130 (0.42%) cases. Clinical confirmation (karyotype for singleton pregnancies, ultrasound for multifetal pregnancies) was available for 58.5% (76/130) of cases. Of the 76 cases with confirmation, 42.1% were vanishing twin, 48.7% were viable twin, 5.3% were diandric triploids, and 3.9% were nontriploid pregnancies that lacked evidence of co-twin demise. One pregnancy had other indications suggesting triploidy but lacked karyotype confirmation. Of the 5 vanishing twin cases with a known date of demise, 100% of losses occurred in the first trimester; up to 8 weeks elapsed between loss and detection by NIPT.

CONCLUSION

This single-nucleotide polymorphism-based NIPT successfully identified vanished twin, previously unrecognized twin, and triploid pregnancies. As vanishing twins are more likely to be aneuploid, and undetected residual cell-free DNA could bias NIPT results, the ability of this method to identify additional fetal haplotypes is expected to result in fewer false-positive calls and prevent incorrect fetal sex calls.

Down syndrome screening in assisted conception twins: an iatrogenic medical challenge

OBJECTIVE

The objective of this study was to provide a critical analysis of the impact of assisted conception on prenatal screening for Down syndrome (DS) in twin pregnancies and the value of various screening modalities for early detection of anomalies.

METHODS

The literature was searched using PubMed and the Cochrane Library focusing on prenatal screening and antenatal care of assisted-conception twin pregnancies.

RESULTS

Serum screening alone is of limited value in detecting aneuploid twins, because the unaffected cotwin can "mask" the abnormal serum results of an affected one. In addition, this test can designate the pregnancy as at high risk but not identify the affected fetus. Nuchal translucency (NT) screening is the best available modality and a highly effective screening method for twin pregnancies. Among twins, NT alone has a 69% DS detection rate, first-trimester combined NT and serum biochemistry has a 72% DS detection rate, and an integrated screen will have an 80% DS detection rate at a 5% FPR. The data in the literature concerning the effect of assisted conception on maternal serum screening markers in twin pregnancies are scarce.

CONCLUSIONS

Down syndrome screening in assisted-conception twins presents clinical and technical challenges. Therefore, assisted-conception twins need close monitoring from conception to delivery, by a practitioner familiar with the available screening modalities and their relative accuracy.

Urinary hCG patterns during the week following implantation

BACKGROUND

Human chorionic gonadotrophin (hCG) is used to monitor pregnancy status. Yet the pattern of hCG excretion in the first week following implantation has not been adequately described. Therefore the aim of this study was to describe the average profile of hCG and its variability during the 7 days following estimated implantation in a population of naturally conceived pregnancies.

METHODS

We measured daily hCG concentrations in first-morning urine for 142 clinical pregnancies from women with no known fertility problems. Mixed-effects regression models were used to estimate the hCG trajectory and its variability in relation to pregnancy outcomes.

RESULTS

hCG rose 3-fold between the day of detection and the next day (95% CI = 2.7-3.4). The relative rate of rise decreased thereafter, reaching 1.6-fold (95% CI = 1.5-1.8) between days 6 and 7. HCG levels followed a log-quadratic trajectory, and the patterns of rise were unrelated to number of fetuses, risk of spontaneous abortion or sex of the baby. Later implantations (after 10 luteal days) produced slower rates of increase.

CONCLUSIONS

Although mean hCG follows a log-quadratic trajectory during the first week of detectability, there is high variability across pregnancies. Later implantation may reflect characteristics of the uterus or conceptus that slow hCG production.

Defining the rise of serum HCG in viable pregnancies achieved through use of IVF

BACKGROUND

We aimed to characterize the rate of HCG rise associated with viable IVF pregnancies, and to evaluate the association between HCG rise and potentially influential factors.

METHODS

We performed a retrospective cohort analysis of all viable pregnancies achieved through IVF at two centres between January 1999 and March 2004.

RESULTS

Of the 455 pregnancies resulting in live births, 391 met inclusion criteria and contributed a total of 1052 HCG values. Using random effects models, the best pattern to describe the rise of log HCG was quadratic with the rate of increase slowing at 24 days post-oocyte retrieval. Limiting the analysis to measurements below the discriminatory zone, the linear model adequately characterized the profile. The average slope was 0.403, yielding a predicted increase of 1.50 (50% increase) in 1 day and 2.24 (124%) in 2 days. In the final model, absolute HCG values, but not rate of rise, were significantly higher for twins and triplets and significantly lower for patients with BMI>30 kg/m2.

CONCLUSIONS

The HCG profile of viable pregnancies conceived with IVF is quadratic with an earlier plateau than has been reported for non-IVF pregnancies. The average rate of rise is comparable to previous estimates in symptomatic spontaneous conceptions.

Does a "vanishing twin" affect first-trimester biochemistry in Down syndrome risk assessment?

OBJECTIVE

The purpose of this study was to evaluate the impact of spontaneous reduction in multifetal pregnancy on first-trimester maternal serum biochemistry.

STUDY DESIGN

We evaluated first-trimester pregnancy associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin levels in singleton euploid pregnancies. Biochemical values in pregnancies with evidence of spontaneous reduction were compared to other singleton pregnancies. Mann-Whitney U, Student t test, Fisher exact test, and logistic regression analysis were used for statistical comparison.

RESULTS

There were 41 cases (0.9%) of spontaneous reduction. Though spontaneous reduction was not associated with different levels of either analyte, reduction within 4 weeks was associated with higher levels of both PAPP-A (1.79 vs 1.18; P = .002) and free beta-hCG (1.28 vs 0.96; P = .03) compared with other pregnancies. Spontaneous reduction was associated with a higher frequency of PAPP-A >95th %ile (17.1 vs 4.7%; P = .003) and free beta-hCG >95th %ile (17.1% vs 5.0%; P = .004). Logistic regression identified independent associations between spontaneous reduction and both high PAPP-A and high free beta-hCG.

CONCLUSION

Recent spontaneous reduction is associated with higher values of PAPP-A and free beta-hCG. These differences have the potential to affect risk assessment for fetal aneuploidy.

The "vanishing embryo" phenomenon in an oocyte donation programme

BACKGROUND

We studied the incidence of vanishing embryos (VE) in pregnancies achieved by oocyte donation and evaluated the obstetric and perinatal complications.

METHOD

A retrospective study was carried out based on a chart review of 399 patients with multiple pregnancies from our oocyte donation programme. We defined vanishing phenomenon as the early resorption, in the first trimester, of one or more embryos in a multiple gestation, after confirming embryonic heart activity by transvaginal ultrasound.

RESULTS

Vanishing embryo was observed in 75 patients (18.8%). In 60 patients (80%) this phenomenon occurred before the ninth gestational week. A higher incidence of VE was observed in patients who initially showed a higher number of gestational sacs (P < 0.03). Vaginal bleeding in the first trimester was significantly higher in patients with VE (P < 0.005). Miscarriage rate was similar in pregnancies with and without VE (P = NS). The incidence of pregnancy induced hypertension was decreased in the group with VE (P < 0.03). Preterm spontaneous rupture of membranes occurred more frequently in pregnancies with VE (P < 0.05). However, gestational age at delivery was similar in the group with VE and the controls.

CONCLUSIONS

The high incidence of VE in pregnancies achieved by oocyte donation should be considered when counselling patients with high order multiple gestations.

Serum levels of intact human chorionic gonadotropin (HCG) and its free alpha and beta subunits, in relation to maternal thyroid stimulation during normal pregnancy

The main objective of the present study was to present additional evidence of the potentially important thyrotropic role of hCG to regulate the maternal thyroid gland during normal pregnancy. Sequential determinations (first and last trimesters) of intact hCG, free alpha and beta-hCG subunits concentrations (using monoclonal IRMAs), and assessment of parameters of thyroid function and thyroid volume were carried out in 62 pregnant women who exhibited during the first trimester of gestation low TSH levels (< or = 0.20 mU/L), and compared to 276 pregnant women with normal TSH levels. The prevalence of having low serum TSH represented 18% of all pregnancies, with almost one half of cases who transiently had undetectable TSH levels. Lowering of TSH was associated with high hCG levels, and occurred primarily during the first trimester. About 10% of women with low TSH presented transient gestational thyrotoxicosis, frequently associated with vomiting. In comparison to control subjects, women with a suppressed serum TSH had significantly and markedly higher intact hCG and free beta-hCG subunit concentrations. The results suggest that TSH reduction may result from a relative oversecretion of both intact hCG and free beta-hCG subunits, compatible with three hypotheses: a) transient overexpression of the beta-hCG gene, leading to enhanced production of hCG heterodimer; b) increased glycosylation of circulating hCG, with in turn a prolonged half life; c) larger syncytiotrophoblast mass with increased hCG production.(ABSTRACT TRUNCATED AT 250 WORDS)

The natural history of multiple pregnancies after assisted reproduction: is spontaneous fetal demise a clinically significant phenomenon?

OBJECTIVE

To determine the rate of spontaneous fetal demise after heartbeats are demonstrated in multiple pregnancies conceived after IVF-ET.

DESIGN

Retrospective case series.

SETTING

University-based IVF-ET program.

PATIENTS

Eighty-one patients in whom initial transvaginal ultrasound (US) study, performed at 5 to 6 weeks of gestation, identified more than one gestational sac. Total number of sacs was 191.

INTERVENTION

Patients were followed by serial US examinations.

MAIN OUTCOME MEASURE

Outcome of pregnancies.

RESULTS

Twenty-four empty gestational sacs were identified in 21 patients, of whom 15 delivered, 2 miscarried, and 4 are currently ongoing beyond first trimester. Of the 167 initially viable embryos, 9 (5%) underwent spontaneous fetal demise. In 5 of these 9 pregnancies, initial US identified significant interfetal size variation.

CONCLUSIONS

The rate of spontaneous fetal demise for a specific embryo in multiple gestation, after fetal heartbeats have been identified in early pregnancy, is 5%. This rate is similar to that seen in spontaneous conceptions. The chance of future fetal demise increases if first trimester interfetal size variation is significant.