Impact of Serum Progesterone Value on Embryo Transfer Timing, and Pregnancy Rate
1. Introduction
Progesterone is one of the steroids hormones, which performs an essential function
in many tissues other than the reproductive system, like in the mammary
gland, to prepare the glands for breastfeeding, the cardiovascular system, central
nervous system and bones. Firstly, progesterone was described as a molecular
formula; yet, only in the mid-1940s, Russell Marker begins to manufacture progesterone
from diosgenin, derived from the Japanese plant Dioscorea tokoro. Progesterone
provides the endometrial transition from a proliferative to the secretary
stage, support embryo development and is vital to pregnancy maintenance [1].
The corpus luteum substantially produces progesterone until the ninth week of
pregnancy; following, the trophoblasts improve progesterone production, to become
the most extensive resource of this hormone after the 12th-week gestation.
Corpus luteum lack appears to happen in 35% of recurrent miscarriage cases.
Progesterone is essentially manufactured from maternal LDL cholesterol through
the placenta by a total enzyme system, and only a tiny portion will produce by
fetal steroid genesis [1]. Progesterone promotes interaction on particular receptors
by inducing tubal motility and impacting endometrial maturation and uterine
vascularization in the pre-implantation phase. Moreover, P4 inhibits the T
lymphocyte-mediated tissue reaction, collectively with human chorionic gonadotrophin
and decidual cortisol. Progesterone appears to produce tocolytic and
immunosuppressive influences in the areas of significant contact within maternal
and fetal compartments.
2. Progesterone Function
P4 is an intrafollicular steroid that performs an essential role in ovulation, implantation,
and pregnancy support and maintenance. P4 is short and elevated
at 18 hours following the luteinizing hormone (LH) surge release; in addition,
P4 is the main content of follicular fluid steroids in mammalian preovulatory
follicles [2] P4 was initially being considered as a contraceptive factor through
reducing the luteinizing hormone surge and ovulation. It has an essential function
in pregnancy maintenance and controlling biological processes in the ovarian
tissue and fetomaternal unit. The processes consist of meiosis resumption,
fertilization, embryonic development and implantation [2]. Clinically, it can be
utilised in the female reproductive system as luteal support during in vitro fertilisation
(IVF), hormone replacement treatment for older women, and as a
treatment for endometriosis and polycystic ovarian syndrome in younger women.
Moreover, P4 has immunological roles for the maintenance of a fetomaternal.
Some researches illustrate that P4 treatment for luteal maintenance in
creased uterine receptivity at the ultrastructure levels and improved mice’s implantation
rate [2]. The function of steroids is to get meiotic support and undergo
regular fertilisation and development to the blastocyst stage. The higher
the ratios of P4 to E2 in follicular fluid in several species, the better embryo
development. In one research, scientists tried to examine the impact of P4 on
the developmental capability of mouse GV oocytes and following fertilisation
potential in concentrations comparable to that of preovulatory follicular fluid.
The results pointed that P4 could not improve the embryo’s fertilisation rate
and development to the blastocyst stage. Other studies have reported similar
results, which indicates that the P4 maturation medium reduced the rate of
blastocyst formation [2]. However, on the other hand, another research showed
that the presence of P4 in the porcine oocyte maturation medium improved
sperm head decondensation and male pronuclei formation; moreover, they found
out that the addition of P4 to the porcine oocyte maturation medium can increase
both fertilisation and cleavage rates, whereas E2 could not [2]. The importance
of sufficient progesterone systemic concentrations through early embryo
development is recommended by several researchers, including supplementation
with exogenous progesterone. Progesterone’s effects can be made both
by a direct impact on the embryo or indirectly via the uterus or possibly both.
As for the direct impact, progesterone receptors (PGRs) (Figure 1) must be
present in the embryo; however, PGRs in mice couldn’t be found until the blastocyst
stage. Therefore, it is most likely for progesterone to affect embryo survival
through an indirect effect on the uterus [3]. The indirect effect of P4 can
impact embryo development by binding to uterine stroma or endometrial PGRs
and starting a process of events containing differences in gene expression; thus,
eventually protein expression or variations in uterine permeability to ions, amino
acids or metabolites from plasma or by non-genomic effects on the uterine
endometrium [3].
Figure 1. Action mechanism of selective progesterone receptor modulators SPRMs, that have
a direct effect on uterine fibroids, endometrium and the pituitary gland; where it binds to the
PR to medicate action either by activation or deactivation [3].
3. Serum Progesterone and Embryo Transfer
Several early studies suggested the importance of luteal phase support in frozen
cycles, which has shown that progesterone’s supplementation does impact the
outcome in frozen embryo transfer. Progesterone (P4) is needed for successful
embryonic implantation into the endometrium and support of the pregnancy in
natural cycles, fresh in vitro fertilization cycles, and frozen embryo transfer (FET)
cycles. Thus, rumours investigation has been done to illustrates the impact and
importance of the P4 in Embry transfer. Therefore, P4 must be supplemented in
order to enhance embryo transfer success and pregnancy rate.
3.1. Progesterone Supplementation Route
and Administration Timing
For P4 supplementation, there are three administration routes, either oral, vaginal
or intramuscular. The oral P4 administration provides inadequately sustained
plasma progesterone concentrations, although plasma progesterone concentration
is a weak marker of bio-availability [4]. Regarding vaginal and intramuscular
administration, it has been reported that intramuscular administration
is more effective than vaginal supplementation [5]. Several factors can change P4
serum levels following vaginal administration, like sexual intercourse, poor patient
appliance, vaginal retention, disposition, and metabolism variations. Low
P4 levels were recorded in more than one-third of patients who had daily vaginal
P4 administration of 600 mg micronized progesterone. However, a high vaginal
P dose of 1200 mg can increase the serum P levels [6]. P4 route of administration
effectiveness can also depends on the other factors, such as age and weight.
For instance, in older women, the vaginal progesterone is more efficient as the
vaginal mucosa of older women is thinner and more atrophic, increasing the
absorption of vaginal progesterone. Moreover, other studies showed that body
weight is an independent factor influencing serum progesterone concentrations
following four days of vaginal progesterone administration. These results are biologically
probable since bodyweight is a vital factor that affects drug absorption,
distribution, metabolism and elimination [7]. P4 can be supplemented through
Gonadotropin-releasing hormone (GnRH) agonists. GnRH agonists enhance GnRH
production, which stimulates stimulating follicle hormone (FSH) and luteinizing
hormone (LH), which excites ovulation and develops corpus luteum, that in return
stimulates P4 production (Figure 2) [8].
Another important aspect to consider in P4 administration is the timing and
duration of the administration. The implantation window is the ideal length of
progesterone supplementation and the growth of maximal endometrial receptivity
which can be determined through endometrial biopsies collection and assessing
presence of pinopodesorby other biomarkers of implantation (e.g., the
expression of @Vb3, PP14, and HOXA 10 gene expression); also it can be determined
through transferring the embryos and examine the pregnancy and implantation
rates. For most ART treatment, progesterone supplement practice is
Figure 2. GnRH action mechanism. P4 is produce through a signaling cascade which starts
from the hypothalamus in the brain till it reaches the gonads to produce P4 [8].
three days before embryo transfer; thus, if an embryo transfer is performed on
Day 3 of development, progesterone supplement should be performed three days
before embryo 3. Therefore, progesterone exposure days and timing before embryo
transfer relay on the frozen embryos’ stage to be transferred. In Sharma and
Majumdar, progesterone supplementation for three days before embryo transfer
(Embry at cleavage stage 4 - 6-cell stage) had significantly higher pregnancy and
implantation rates than four days of progesterone administration. Therefore,
they concluded that progesterone supplementation for three days before embryo
transfer had better pregnancy and implantation rates (Figure 3) [9].
3.2. Progesterone Level and Embryo Transfer
P has a fundamental function in the endometrial transformation before frozen
embryo transfer (FET). Endometrial transformation can be accomplished through
natural cycle or via an artificial endometrial preparation [10]. Natural endometrial
transformation requires no external medication, where corpus luteum secrete
endogenous progesterone in an ovulatory cycle and, thus making this approach
preferable to some patients. In artificial endometrial transformation, external
administration of exogenous estrogen and progesterone is applied to accomplish
both adequate endometrial priming and serum hormonal values approaching
the natural ovulatory cycle [10]. Progesterone serum level is vital to
achieve successful implementation and pregnancy rate on the day of embryo
transfer, several studies investigate abnormal P4 serum level (low and elevated level),
and their impact on embryo transfer, pregnancy rate, and live birth. In one
study, a significant association was reported among positive pregnancy outcome
and progesterone level at the day of hCG trigger were 79.2% of a female with
positive pregnancy at progesterone level < 1.5, while 9.3% of a female with positive
pregnancy at progesterone level > 2.5. In addition, 1107 women get pregnant
when level of progesterone < 1.5 ng/mL, 127 get pregnant at level of 1.5 - 2 ng/
ml, 70 get pregnant at level of >2 - 2.5 ng/ml (Table 1) [11].
Moreover, Gaggiotti-Marre et al . study showed the importance of serum levels
on the day prior to FET in women undergoing a natural endometrial preparation
cycle; their results indicated that low serum P levels on the day before embryo
transfer (<10 ng/ml) are correlated with significantly lower clinical pregnancy
rate and live birth rate. Also, low serum P4 level was associated with higher miscarriage
rates were (Figure 4) [11].
Similar results to the above studies have been reported, which showed that patients
with an artificial endometrial preparation cycle using vaginal progesterone
had a significantly reduced ongoing pregnancy rate, as the serum, P was < 9.2
ng/ml on the day of embryo transfer [12]. Moreover, Labarta et al ., observation
point out no association for endometrial volume with either serum P levels or
ongoing pregnancy rate, which implies if a minimal endometrial thickness is obtained,
serum P levels would be the primary, more predictable marker for pregnancy
more than ultrasound endometrium evaluations. Therefore, a minimal
serum P threshold on the day of embryo transfer should be reached for a successful
ongoing pregnancy rate [12]. The retrospective performed by Santos-
Ribeiro et al ., 2014, also evaluates the effect of low progesterone on the live-birth
rate. The study conducted several evaluations according to various ordinal and
normal progesterone levels (≤0.50, 0.50 - 0.75, 0.75 - 1.00, 1.00 - 1.25, 1.25 -
1.50, >1.50 ng/ml)” to compare the difference in live birth percentage. According
to the previous serum progesterone levels, the live birth rates were 17.1%, 25.1%,
26.7%, 25.5%, 21.9% and 16.6%. The results confirm earlier studies conclusion
by finding the association between low P4 level and low birth rate [13]. Moreover,
all patients had the same dose of exogenous FSH similar to the regular P
group; they were also simulated using the same hCG criteria and had unaffected
maturation and fertilization rates. Hence, the low birth weight associated with a
low P4 level does not appear to be related to inadequate stimulation or poorer
oocyte maturation or fertilization competence [13]. Throughout controlled ovarian
hyperstimulation (COH), progesterone serum elevation is always avoided
through suppressing luteinizing hormone (LH) secretion by administrating a
gonadotropin releasing hormone (GnRH) agonist or antagonist. Therefore, various
researches have been performed to record and evaluate elevated P4 impact
on embryo transfer and pregnancy rate. A research examined the incidence of
premature progesterone elevations in frozen-thawed embryo transfer cycles and
the association with any adverse impacts on clinical outcomes. The elevated serum
progesterone level was 4.6 nmol/l or higher in over one-fifth of patients
undergoing IVF treatment. The results indicated no difference in clinical pregnancy
rate, and ongoing pregnancy rate was seen within patients with and without
elevated progesterone [14]. However, it has been demonstrated that High P level
prior to oocyte collection is linked with a noticeable endometrial receptivity reduction.
Also, definitely the gene expression profile of the endometrium will be
affected when P level is higher than its normal level at the end of the follicular
phase. Elevated P levels on the day of hCG throughout the first fresh cycle are
associated with poor pregnancy rate, although not in following frozen-thawed
embryo transfer cycles [15]. This finding has been supported by Ibrahim et al .,
where they demonstrate that the impact of elevated P4 can be extended to the
level of fetal development itself and results in lower birth weights. The study also
recommends that the progesterone on the day of hCG administration may be
reasonable to delay the transfer in such circumstances. The research also points
out that high progesterone on the day of hCG administration can be lined with
various vascular endothelial growth factor expression in the endometrium. Accordingly,
this can alter endometrial receptivity, ending in reduced implantation.
Thus, it has been reported that that elevated progesterone can be correlated with
adverse perinatal results [16]. Moreover, in one of the respective researches, they
assessed whether the hormone administration following the end of menstruation
and till the day of hCG administration in GnRH antagonist/recombinant FSH
cycles would be associated with pregnancy rate. The results suggested that elevated
P4 serum level through the menstruation-free interval is correlated with a
reduced likelihood of ongoing pregnancy [17]. The impaired influence of high P
exposure on pregnancy rate can be assigned to the increase and premature expression
of P4 receptors on the endometrium in stimulated IVF cycles, which
has been linked with the elevated E2 concentration through the follicular phase
in these cycles [17]. Furthermore, in the Bosch et al ., study where they also evaluate
elevated progesterone, they demonstrated no inverted association between
ongoing pregnancy rates and serum progesterone levels on the day of hCG administration.
In patients with elevated progesterone serum levels, < or =1.5 ng/
mL, significantly higher ongoing pregnancy rates were recorded in comparison
with patients with normal serum progesterone levels > 1.5 ng/mL (31.0% vs 19.1%;
P = 0.00006); the odds ratio was 0.53, with a 95% confidence interval of 0.38 to
0.72 [18]. The study also showed that elevated progesterone could be caused by
an increase in a daily dosage of follicle-stimulating hormone, the number of oocytes
collected, and estradiol (E2) values on the day of hCG administration. Additionally,
women treated with GnRH agonists had significantly higher serum
progesterone levels than those receiving GnRH antagonists (0.84 ± 0.67 vs 0.75 ±
0.66 ng/mL; P = 0.0003) [18]. Finally, Ochsenkühn et al ., also confirmed the
above researches finding by proposing that high follicular P promotes the endometrium,
and hence the replacement of a day-3 embryo in an asynchronous
endometrium point out a failure of establishing embryo-endometrium cross-dialogue,
this leading to embryo death and implementation failure. The study pro
posed that women who were experiencing pituitary down-regulation in addition
to COH with by GnRH agonists and 5 days following collection display a significantly
reduced live birth rate in the case of a slight P4 rise on the day of hCG
administration [1].
3.3. Why Optimal P4 Level Is Vital
Low serum progesterone can be a factor of low pregnancy rate; thus, this can be
more serious with patients who already have low P4 in their blood circulation.
According to González-Foruria et al ., study, it has been found that certain factors
affect progesterone concentrations on the day before embryo transfer, which
can alter pharmacokinetics such as age, weight, and prior history of low progesterone
concentrations, however other factors such as the timing of blood sampling
do not depend on differences in drug absorption [7]. In addition, high P4
serum level has been High P level before eggs collection is linked with a noticeable
endometrial receptivity decrease. The endometrium’s gene expression profile
at the end of the follicular phase is certainly altered when the P level is above 1.5
ng/ml [15]. Progesterone importance in successful pregnancy rate and implementation
rate have been clearly illustrated, however, significant progesterone
elevation prior to hCG injection can point to a desynchronization within the endometrium
and the embryo through reducing pregnancy rates [14]. In summary, a
successful implantation needs a competent blastocyst synchronization with a receptive
endometrium, which is mainly coordinated by the endometrium receptivity
are estrogen and progesterone. Thus, an optimal P4 level is essential for
successful implantation and pregnancy [15].
4. Conclusion
Progesterone is essential for establishing and maintaining embryo implantation
and pregnancy; also, P4 is used for luteal phase deficiency in infertility treatment.
Yet, progesterone therapy’s optimal timing and dose can influence the impact
of P4 on pregnancy. Also, low or elevated P4 level can negatively impact
embryo transfer timing and pregnancy rate.
Acknowledgements
Objective of the Association for Scientific Research of the IRIFIV-AISRG Group
(IRIFIV-AISRG),Research foundation in Casablanca, Maintaining consistent and
reliably high success rates is a monthly challenge for in IVF labs, the IRIFIV Fertility
Center in Casablanca—Morocco Department of Reproductive Medicine and
Reproductive Biology and Embryology, advocacy of interdisciplinary Department
of Reproductive Medicine and Reproductive Biology and Embryology study, encompassing
the areas of research, collections and publishing Articles.
Conflicts of Interest
The authors declare no conflicts of interest.
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Abbreviations
In-vitro fertilization (IVF)
luteinizing hormone (LH)
progesterone receptors (PGRs)
selective progesterone receptor modulators (SPRMs)
frozen embryo transfer (FET)
Gonadotropin-releasing hormone (GnRH)
follicle hormone (FSH)
estradiol (E2)