Elective single embryo transfer and perinatal outcomes: a systematic review and meta-analysis

Low dose of rFSH [100 IU] in controlled ovarian hyperstimulation response: a pilot study

Background

The initial dose of recombinant Follicle Stimulating Hormone [rFSH] to be used in assisted reproduction treatment depends on several factors, mainly the cause of the infertility and the patient’s age. For young patients [≤35 years] usually an initial dose of around 150 IU of rFSH is recommended, but there are no studies proving that this should actually be the standard initial dose. We aimed to report the experience of a low-cost Human Reproduction Center where a dose of 100 IU of rFSH was used for controlled ovarian hyperstimulation [COH].

Findings

An observational prospective study was performed on 212 women aged ≤38 years old that underwent high-complexity assisted reproduction treatments. The patients’ infertility was mainly caused by tuboperitoneal, idiopathic or male factors. Controlled ovarian stimulation was performed using 100 IU of rFSH. Regarding the COH, 53.8% of the patients presented a satisfactory response, 25.9% low response, 14.2% hyper-response, and 6.1% developed ovarian hyperstimulation syndrome. Of the 55 patients with poor response, 20 started a new cycle with an initial dose of 200 IU of rFSH; 65% showed a satisfactory response, 10% a poor response, 20% a hyper-response, and 5% developed OHSS.

Conclusion

The initial dose of 100 IU of rFSH was considered adequate for controlled ovarian hyperstimulation, meeting the aim to reduce the costs of the assisted reproduction treatment.

[How far can we go to oocyte donation? Debates on the risks of late pregnancies]

In France, there is a decline in first-time motherhood influenced by many sociocultural factors thus leading to a reproductive age where fertility decreases and which increase the risks associated with late pregnancy. The oocyte donation in France is subject to The Bioethic law granting no support in infertility beyond past 43 years. Thus, to satisfy their need for maternity, the French use a gift abroad. Then we will report the case of a pregnancy obtained by an oocyte donation, after 42 years, which was complicated. We will discuss the importance of taking into account the risk factors before a support to ART, and the ethical issues raised by this case. After a brief review of French legislative framework governing the practice of oocyte donation, we will evoke ways to improve the coverage needs of it in France.

Socioeconomic status affects the prevalence, but not the perinatal outcomes, of in vitro fertilization pregnancies

STUDY QUESTION

Does maternal socioeconomic status (SES) confound or modify the association between IVF and perinatal outcome among singleton births?

SUMMARY ANSWER

There were substantial socioeconomic differences in the frequency of IVF pregnancies, but maternal SES was not associated with the outcome of IVF pregnancies.

WHAT IS KNOWN ALREADY

The use of IVF is associated with SES. Additionally, women with lower SES tend to have an increased risk of adverse perinatal outcomes such as preterm birth and small for gestational age birth.

STUDY DESIGN, SIZE, DURATION

We conducted a population-based cohort study using the Finnish Medical Birth Register (2006-2010).

PARTICIPANTS/MATERIALS, SETTING, METHODS

We analyzed the total population of singleton births in Finland (n = 291 004) and then compared the unadjusted and adjusted incidences of adverse perinatal outcomes for singleton births after IVF (n = 5647) and non-IVF pregnancies (n = 285 357) in relation to SES.

MAIN RESULTS AND THE ROLE OF CHANCE

SES did not confound or modify the association between IVF and perinatal outcomes after adjustments for age, parity, smoking, gestational diabetes, maternal diabetes and pre-eclampsia. However, the prevalence of IVF pregnancies increased with SES; on average 1.9% of singleton infants were born after IVF pregnancies, while the corresponding percentages were 3.2 and 1.2% for the highest and lowest SES strata, respectively. IVF was statistically significantly associated with 1.27-, 1.49-, 1.63-, 1.47-, 1.35-, 1.40-, 4.97- and 1.14-fold higher incidences of admission to a neonatal unit, stillbirth, preterm birth, low birthweight, low Apgar scores (<7 at 5 min), Cesarean section, placenta previa and major congenital anomaly, respectively. Irrespective of the SES group, women who became pregnant through IVF were older and more often nulliparous and non-smokers compared with women with non-IVF pregnancies.

LIMITATIONS, REASONS FOR CAUTION

The occupation of 22% of the women was unknown and that of a further 25% did not match any of the criteria for our SES strata. Additionally, infertility is a problem for couples but the definition of SES in this study was based only on the mother's occupation at the time of birth.

WIDER IMPLICATIONS OF THE FINDINGS

The prevalence of IVF-conceived pregnancies was highest among the highest SES group, but SES did not confound the perinatal outcomes of IVF pregnancies after adjusting for background factors. However, the magnitude of risks associated with the IVF technique itself may be more significant than previously thought.

STUDY FUNDING/COMPETING INTEREST(S)

None of the authors received any funding specifically for this study, and we have no competing interests.

Birthweight and placental weight; do changes in culture media used for IVF matter? Comparisons with spontaneous pregnancies in the corresponding time periods

STUDY QUESTION

Have changes in culture media used for IVF resulted in changes in offspring birthweight or placental weight that differed from the trends in offspring from spontaneous conceptions during the corresponding time periods?

SUMMARY ANSWER

Changes in culture media used for IVF were associated with significant differences in offspring birthweight and in placental weight to birthweight ratio when compared with the trend in offspring from spontaneous conceptions during the time periods.

WHAT IS KNOWN ALREADY

The effect of culture media used for IVF on offspring birthweight has varied between studies. There is a large variation in birthweight between newborns, and birthweight may vary across populations and over time. Such variations may therefore have influenced previous results.

STUDY DESIGN, SIZE, DURATION

We included all singleton births from IVF at one treatment center in Norway during the years 1999-2011(n = 2435) and all singleton births from spontaneous conceptions in Norway during the same years (n = 698 359).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Three different media were used for embryo culture; Medicult Universal IVF (1999 through 2007, n = 1584), Medicult ISM1 (2008 until 20 September 2009, n = 402) and Vitrolife G-1 PLUS (21 September 2009 through 2011, n = 449). We estimated mean birthweight and placental weight in IVF pregnancies by culture media. We also estimated mean weights in IVF and in spontaneous pregnancies by year of birth. Thereafter, we studied whether the changes in mean weights in IVF pregnancies differed from the changes in weight in spontaneous pregnancies in the periods corresponding to culture media changes by applying a grouped difference-in-difference analysis. Adjustments were made for parity, maternal age and gestational age at birth.

MAIN RESULTS AND THE ROLE OF CHANCE

In singleton offspring from IVF the mean birthweight was 3447.6 g with Medicult Universal, 3351.7 g with Medicult ISM1 and 3441.4 g with Vitrolife G-1 PLUS (P < 0.05). The corresponding mean placental weights were 684.1, 693.4 and 704.3 g (P < 0.05). In offspring from spontaneous conceptions the mean birthweight decreased (56.9 g) and the placental weight increased (9.3 g) during the study period. The adjusted difference in birthweight in offspring from IVF decreased with 35.0 g by the change from Medicult Universal to Medicult ISM1 (P = 0.16) and increased with 79.9 g by the change from Medicult ISM1 to Vitrolife G-1 PLUS (P = 0.01) when compared with changes in offspring after spontaneous conceptions, We also found a significant increase in placental weight in relation to birthweight by the change from Medicult ISM1 to Vitrolife G-1 PLUS (P = 0.02).

LIMITATIONS, REASONS FOR CAUTION

There may be underlying factors that have influenced both birthweight and the use of culture media in IVF pregnancies. Lack of adjustment for such possible factors may have biased our results.

WIDER IMPLICATIONS OF THE FINDINGS

We found a significant effect of culture media used for IVF on birthweight and on placental weight in relation to birthweight. Also the population changes over time should encourage identification of factors in very early embryonic life that may influence birthweight and placental weight.

STUDY FUNDING/COMPETING INTERESTS

We received funding from the South-Eastern Regional Health Authority in Norway for this study (2011136-2012). None of the authors has any conflicts of interest to declare.

Social disparity affects the incidence of placental abruption among multiparous but not nulliparous women: a register-based analysis of 1,162,126 singleton births

OBJECTIVES

To identify risk factors for placental abruption and to evaluate associations between adverse perinatal outcomes and placental abruption stratified by parity among women with singleton births from 1991 to 2010 in Finland.

STUDY DESIGN

A retrospective population-based case-control study of singleton births in Finland from 1991 to 2010 (n=1,162,126 from the Finnish Medical Birth Register). We modelled the group-specific risk factors for placental abruption in unadjusted and adjusted models.

RESULTS

In total 3.5 and 3.7 per 1000 nulliparous and multiparous women, respectively, were affected by placental abruption. The recurrence rate was 8.6 per 1000 births. The adjusted risk for placental abruption increased in pregnancies characterised by advanced maternal age, low birth weight, smoking, major congenital anomaly, preeclampsia and male foetal sex in both parity groups. In vitro fertilisation increased the risk only in nulliparae whereas anaemia, a prior caesarean section and the lowest socioeconomic status increased the risk in multiparae. Births affected by placental abruption were associated with an increased admission for neonatal intensive care, preterm birth, low birth weight (<2500 g), small for gestational age infants, low Apgar scores, and low newborn umbilical vein pH (<7.15). Placental abruption resulted in increased risks of stillbirth and early neonatal death in both parity groups.

CONCLUSIONS

The burden of placental abruption is equal in nulliparae and multiparae, but risk factors vary substantially. Social disparity only affects the incidence of placental abruption among multiparous women, indicating that factors related to lifestyle and health behaviour have different effects on the parity groups.

The multiple birth epidemic: revisited

The modern era of infertility treatment was heralded over half a century ago with the introduction of new hormonal drugs that could effectively induce ovarian ovulation. However, it was quickly recognized that the birth of these new "miracle drugs" was associated with a remarkable increase in the incidence of high-order multiple births. Despite the fantastic improvement in our ability to monitor ovarian response during ovulation induction, and our power to control the number of embryos introduced into the womb through IVF, multiple births remain a leading cause of long-term child morbidity among infertility patients. Efforts to prevent what was coined in the 1960s as the "multiple birth epidemic" remain an urgent concern. A new body of research clearly points at our capacity to reduce the risk of multiple births and their associated long term morbidity without diminishing current high success rates of infertility treatment.

Refuting a misguided campaign against the goal of single-embryo transfer and singleton birth in assisted reproduction

Much recent progress has been made by assisted reproductive technology (ART) professionals toward minimizing the incidence of multiple pregnancy following ART treatment. While a healthy singleton birth is widely considered to be the ideal outcome of such treatment, a vocal minority continues a campaign to advocate the benefits of multiple embryo transfer as treatment and twin pregnancy as outcome for most ART patients. Proponents of twinning argue four points: that patients prefer twins, that multiple embryo transfer maximizes success rates, that the costs per infant are lower with twins and that one twin pregnancy and birth is associated with no higher risk than two consecutive singleton pregnancies and births. We find fault with the reasoning and data behind each of these tenets. First, we respect the principle of patient autonomy to choose the number of embryos for transfer but counter that it has been shown that better patient education reduces their desire for twins. In addition, reasonable and evidentially supported limits may be placed on autonomy in exchange for public or private insurance coverage for ART treatment, and counterbalancing ethical principles to autonomy exist, especially beneficence (doing good) and non-maleficence (doing no harm). Second, comparisons between success rates following single-embryo transfer (SET) and double-embryo transfers favor double-embryo transfers only when embryo utilization is not comparable; cumulative pregnancy and birth rates that take into account utilization of cryopreserved embryos (and the additional cryopreserved embryo available with single fresh embryo transfer) consistently demonstrate no advantage to double-embryo transfer. Third, while comparisons of costs are system dependent and not easy to assess, several independent studies all suggest that short-term costs per child (through the neonatal period alone) are lower with transfers of one rather than two embryos. And, finally, abundant evidence conclusively demonstrates that the risks to both mother and especially to children are substantially greater with one twin birth compared with two singleton births. Thus, the arguments used by some to promote multiple embryo transfer and twinning are not supported by the facts. They should not detract from efforts to further promote SET and thus reduce ART-associated multiple pregnancy and its inherent risks.

IVF and breast cancer: a systematic review and meta-analysis

BACKGROUND

The effects of controlled ovarian hyperstimulation (COH) for IVF in terms of breast cancer risk remain controversial, despite the hormone-dependent nature of the latter.

METHODS

Eligible studies up to 15 February 2013 were identified and pooled effect estimates for relative risk (RR) were calculated separately for the investigations using the general population and those using infertile women, as a reference group. Fixed- or random-effects models were implemented and subgroup analyses were performed, as appropriate.

RESULTS

Eight cohort studies were synthesized, yielding a total cohort size of 1,554,332 women among whom 14,961 incident breast cancer cases occurred, encompassing 576 incident breast cancer cases among women exposed to IVF. No significant association between IVF and breast cancer was observed either in the group of studies treating the general population (RR = 0.91, 95% confidence interval (CI): 0.74-1.11) or infertile women (RR = 1.02, 95% CI: 0.88-1.18), as a reference group. Of note were the marginal associations, protective for pregnant and/or parous women after IVF (pooled effect estimate = 0.86, 95% CI: 0.73-1.01) and adverse for women <30 years at first IVF treatment (pooled effect estimate = 1.64, 95% CI: 0.96-2.80).

CONCLUSIONS

At present, COH for IVF does not seem to impart increased breast cancer risk. Longer follow-up periods, comparisons versus infertile women, subgroup analyses aiming to trace vulnerable subgroups, adjustment for various confounders and larger informative data sets are needed before conclusive statements for the safety of the procedure are reached.

Maternal, perinatal and long-term outcomes after assisted reproductive techniques (ART): implications for clinical practice

The use of assisted reproductive techniques (ART) is on the rise throughout the world and the number of babies born as a result of ART has reached an estimated total of 5 million since the world's first, Louise Brown, was born in 1978. Data from many prospective and retrospective studies have suggested increased risks of adverse maternal, perinatal and long-term outcomes after ART compared to natural conception. Recent research suggests that underlying maternal factors rather than ART methods themselves play a significant role in causing such outcomes. Couples attempting ART need to be provided with accurate and reliable information on risks of adverse reproductive outcomes and reassured that absolute risks appear small. Clinicians need to remain vigilant about increased risk of pregnancy complications and formulate a plan of care for the woman, from periconception to the puerperium, which aims to prevent or minimise maternal and perinatal morbidity. This review attempts to summarise the available data on reproductive outcomes after ART and provide guidance to the obstetricians and primary care physicians about management of ART pregnancies.

The impact of single embryo transfer policy on pregnancy outcomes after legislative change

We evaluated the effect of mandatory single embryo transfer (SET) on live birth rates and pregnancy outcomes in Turkey. A retrospective study was conducted in Zekai Tahir Burak Women's Health Education and Research Hospital. Four hundred and four patients undergoing intracytoplasmic sperm injection (ICSI) cycles were included in the study. In Turkey, the number of embryos to be transferred in an assisted cycle was limited to three under normal circumstances until 6 March 2010. After that, new legislation was introduced to promote the application of SET. Outcomes were compared in periods of 1 year before and after the new law. We compared pregnancy outcomes of all assisted reproductive cycles in SET cycles (group 1: n = 281) with double embryo transfer (DET) cycles (group 2: n = 123). There were significant differences in oocyte number, multiple pregnancy, gestational age, birth weight and perinatal fetal morbidity between the groups (p = 0.023, 0.001, 0.001, 0.001, 0.001, respectively). But there were no differences in age, baseline FSH, infertility period, stimulation protocol, stimulation day, gonadotrophin dose, clinical pregnancy rate, abortion rate, live birth rate and cesarean rate (p > 0.05). These results suggest that under the new legislation multiple pregnancy rates and perinatal complications are significantly reduced without causing a significant decline in the pregnancy rates.

Reproductive outcomes after assisted conception

The last three decades have witnessed a dramatic increase in the use of assisted reproductive technology (ART) so that now, in developed countries, 1.7% to 4.0% of all children are born after ART. Although absolute risks appear small, data from prospective and retrospective studies indicate increased risks of adverse maternal and perinatal outcomes after ART as compared with spontaneous conception. Recent studies suggest that underlying maternal factors and subfertility play an important role in some of these outcomes rather than the ART procedure itself. A significant risk of assisted conception is multiple pregnancies, but even singleton pregnancies achieved by ART are at a higher risk of hypertensive disease, diabetes, prematurity, low birth weight, and perinatal mortality even after adjusting for confounders. Couples undergoing ART procedures should be counseled in advance regarding increased risks of pregnancy complications and higher rates of obstetric interventions. Although conflicting data exist, studies of children born from ART suggest increased rates of congenital malformations, imprinting disorders (Beckwith-Wiedemann syndrome and Angelman syndrome), and marginally increased risk of cancer. However, the current evidence is inadequate, and prospective long-term studies are needed to eliminate the effect of confounders and draw definite conclusions about the long-term outcomes after ART. The absolute risk of imprinting disorders remains small, and routine screening is not recommended at present. The long-term outcomes after ART are difficult to evaluate because of the variability in ART methods and data reporting, and there is a need for standardized methodology for follow-up after ART.

Neonatal risks from in vitro fertilization and delayed motherhood

Delayed childbearing (DC) is common in most Western countries. The average age of first-time mothers increased in United States from 21.4 years in 1970 to 25.0 years in 2006 and from 25.4 to 30.8 years in Australia in the same period. It is commonly believed that this has no ominous consequences. But several negative consequences of this behavior are described: stillbirth, prematurity, twins, birth anomalies. Age also decreases women’s fertility, thus many couples undergo in vitro fertilization. And we highlight a paradox: medical reproduction techniques decreases their effectiveness with maternal age, but their availability can be an incentive to postpone parenthood. Of course the risks of delayed parenthood involve a minority of cases, but are parents entitled to accept any risk on the behalf of their baby A complete information would make people cautious before deciding to postpone childbearing, though this is often an obliged rather that a free choice: the consumerist society pressure and the difficulty to find an employment have their heavy weight in this choice. But if this choice is not really free, people’s interest is to overcome these pressures and to claim for a real broad choice on when becoming parent, despite the pressures made by their cultural environment to postpone parenthood. Moreover, even reproductive techniques have some risks. Unfortunately, mass media often praise and endorse DC, disregarding the increase of premature babies born because of DC, a real alarm for public health. Pediatricians should discourage the culture that makes DC a normal event.

(1)H NMR based profiling of spent culture media cannot predict success of implantation for day 3 human embryos

BACKGROUND

Identification of a non-invasive technique to assess embryo implantation potential in assisted reproduction would greatly increase success rates and lead more efficiently to single embryo transfer. Early studies suggested metabonomic analysis of spent culture media could improve embryo selection. The goal of this study is to assess if embryo implantation can be predicted based on proton nuclear magnetic resonance ((1)H NMR) profiles of spent embryo culture media from patients undergoing transfer of multiple embryos on cycle day 3.

METHOD

We conducted a retrospective study in an academic assisted reproduction technology (ART) program and analyzed the data in a university research center. Two hundred twenty-eight spent culture media samples originating from 108 patients were individually analyzed. Specifically, five distinct sets (1 to 5) of different types of spent media samples (volume ~14 μL) from embryos that resulted in clinical pregnancy (positive heart rate at 6 weeks gestation) (n (1) = 29; n (2) = 19; n (3) = 9; n (4) = 12; n (5) = 33; n (total) = 102) and from embryos that did not implant (n (1) = 28; n (2) = 29; n (3) = 18; n (4) = 15; n (5) = 36; n (total) = 126) were collected on day 3 of embryo growth. The media samples were profiled using (1)H NMR spectroscopy, and the NMR profiles of sets 1 to 5 were subject to standard uni- and multi-variate data analyses in order to evaluate potential correlation of profiles with implantation success.

RESULTS

For set 1 of the media samples, a borderline class separation of NMR profiles was obtained by use of principal component analysis (PCA) and logistic regression. This tentative class separation could not be repeated and validated in any of the other media sets 2 to 5.

CONCLUSIONS

Despite the rigorous technical approach, (1)H NMR based profiling of spent culture media cannot predict success of implantation for day 3 human embryos.

Genetic polymorphisms influence the ovarian response to rFSH stimulation in patients undergoing in vitro fertilization programs with ICSI

INTRODUCTION

Obtaining an adequate number of high-quality oocytes is a major challenge in controlled ovarian hyperstimulation (COH). To date, a range of hormonal and clinical parameters have been used to optimize COH but none have significant predictive value. This variability could be due to the genetic predispositions of single-nucleotide polymorphisms (SNPs). Here, we assessed the individual and combined impacts of thirteen SNPs that reportedly influence the outcome of in vitro fertilisation (IVF) on the ovarian response to rFSH stimulation for patients undergoing intracytoplasmic sperm injection program (ICSI).

RESULTS

Univariate analysis revealed that only FSHR, ESR2 and p53 SNPs influenced the number of mature oocytes. The association was statistically significant for FSHR (p=0.0047) and ESR2 (0.0017) in the overall study population and for FSHR (p=0.0009) and p53 (p=0.0048) in subgroup that was more homogeneous in terms of clinical variables. After Bonferroni correction and a multivariate analysis, only the differences for FSHR and ESR2 polymorphisms were still statistically significant. In a multilocus analysis, only the FSHR and AMH SNP combination significantly influenced oocyte numbers in both population (p<0.01).

DISCUSSION

We confirmed the impact of FSHR and ESR2 polymorphisms on the IVF outcome. Furthermore, we showed for the first time that a p53 polymorphism (which is already known to impact embryo implantation) could influence the ovarian response. However, given that this result lost its statistical significance after multivariate analysis, more data are needed to draw firm conclusions. Only the FSHR and AMH polymorphism combination appears to influence mature oocyte numbers but this finding also needs to be confirmed.

MATERIALS AND METHODS

A 13 gene polymorphisms: FSHR(Asn680Ser), p53(Arg72Pro), AMH(Ile49Ser), ESR2(+1730G>A), ESR1(-397T>C), BMP15(-9C>G), MTHFR1(677C>T), MTHFR2(1298A>C), HLA-G(-725C>G), VEGF(+405G>C), TNFα(-308A>G), AMHR(-482 A>G), PAI-1 (4 G/5 G), multiplex PCR assay was designed to genotype women undergoing ICSI program. We analyzed the overall study population (n=427) and a subgroup with homogeneous characteristics (n=112).

Trends and factors associated with the Day 5 embryo transfer, assisted reproductive technology surveillance, USA, 2001-2009

STUDY QUESTION

What characteristics are associated with a Day 5 embryo transfer?

SUMMARY ANSWER

The use of the Day 5 embryo transfer has increased over time, with clinicians allowing women with typically 'poorer' prognostic characteristics to undergo a Day 5 embryo transfer. The mean number of embryos per Day 5 transfer decreased from 2001 to 2009, although the prevalence of the Day 5 single embryo transfer remains low and the rate of multiple births remains substantial.

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

Day 5 embryo transfer may reduce the rate of multiple gestation pregnancy. US trends over time in the prevalence of the Day 5 transfer, changes in characteristics of patients receiving Day 5 transfer, and number of embryos transferred are unknown.

DESIGN

We used 2001-2009 US National assisted reproductive technology (ART) Surveillance System (NASS) data on 620,295 fresh IVF cycles derived from autologous oocytes with a Day 3 or 5 embryo transfer. Trends in the mean number of embryos transferred from 2001 to 2009 were assessed by the day of transfer. For 349,947 cycles from clinics performing both Days 3 and 5 embryo transfers, multivariable logistic regression was used to determine the characteristics associated with the Day 5 embryo transfer. We also compared the characteristics of the Day 5 embryo cycles in 2001 and 2009.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, the proportion of ART cycles using the Day 5 embryo transfer increased from 12% in 2001 to 36% in 2009 (P<0.0001), while the mean number of embryos transferred decreased from 2.4 to 2.1 (P<0.0001). Among Day 5 transfers, the rate of the single embryo transfer tripled from 4.5% in 2001 to 14.8% in 2009 (P<0.0001); and the rate of multiple births decreased from 44.8 to 41.1% (P<0.0001). In cycles initiated after 2001, maternal age<35 years, no prior ART cycles, ≥1 prior pregnancies, baseline follicle stimulating hormone<10 international units and ≥10 oocytes retrieved were associated with the Day 5 embryo transfer. Compared with 2001, in 2009, a broader range of candidates received the Day 5 transfer. BIAS Women undergoing multiple ART cycles over time are not linked.

CONFOUNDING FACTORS AND OTHER REASONS FOR CAUTION

We ran multivariable logistic regression to lessen the effects of the confounding factors. Cycle cancelation rates by the day of embryo transfer are unknown.

GENERALIZABILITY TO OTHER POPULATIONS

Generalizable to ART clinics included in NASS.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by the Centres for Disease Control. The authors have no competing interests to declare.