the likelihood of conception decreases and the chance of miscarriage increases. with increasing paternal age, especially 50 years and older, the rate of blastocyst formation decreases. tobacco smoking reduces the chances of ivf producing a live birth by 34% and increases the risk of an ivf pregnancy miscarrying by 30%. a body mass index (bmi) over 27 causes a 33% decrease in likelihood to have a live birth after the first cycle of ivf, compared to those with a bmi between 20 and 27. also, pregnant females who are obese have higher rates of miscarriage, gestational diabetes, hypertension, thromboembolism and problems during delivery, as well as leading to an increased risk of fetal congenital abnormality. ideal body mass index is 19–30. salpingectomy or laparoscopic tubal occlusion before ivf treatment increases chances for women with hydrosalpinges. success with previous pregnancy and/or live birth increases chances low alcohol/caffeine intake increases success rate the number of embryos transferred in the treatment cycle embryo quality some studies also suggest that autoimmune disease may also play a role in decreasing ivf success rates by interfering with the proper implantation of the embryo after transfer. aspirin is sometimes prescribed to women for the purpose of increasing the chances of conception by ivf, but as of 2016 there was no evidence to show that it is safe and effective. a 2013 review and meta analysis of randomised controlled trials of acupuncture as an adjuvant therapy in ivf found no overall benefit, and concluded that an apparent benefit detected in a subset of published trials where the control group (those not using acupuncture) experienced a lower than average rate of pregnancy requires further study, due to the possibility of publication bias and other factors. a cochrane review came to the result that endometrial injury performed in the month prior to ovarian induction appeared to increase both the live birth rate and clinical pregnancy rate in ivf compared with no endometrial injury. there was no evidence of a difference between the groups in miscarriage, multiple pregnancy or bleeding rates. evidence suggested that endometrial injury on the day of oocyte retrieval was associated with a lower live birth or ongoing pregnancy rate. intake of antioxidants (such as n-acetyl-cysteine, melatonin, vitamin a, vitamin c, vitamin e, folic acid, myo-inositol, zinc or selenium) has not been associated with a significantly increased live birth rate or clinical pregnancy rate in ivf according to cochrane reviews. the review found that oral antioxidants given to men in couples with male factor or unexplained subfertility may improve live birth rates, but more evidence is needed. a cochrane review in 2015 came to the result that there is no evidence identified regarding the effect of preconception lifestyle advice on the chance of a live birth outcome. method a graphic explaining the details of ivf. theoretically, ivf could be performed by collecting the contents from the fallopian tubes or uterus after natural ovulation, mixing it with sperm, and reinserting the fertilised ova into the uterus. however, without additional techniques, the chances of pregnancy would be extremely small. the additional techniques that are routinely used in ivf include ovarian hyperstimulation to generate multiple eggs, ultrasound-guided transvaginal oocyte retrieval directly from the ovaries, co-incubation of eggs and sperm, as well as culture and selection of resultant embryos before embryo transfer into a uterus. ovarian hyperstimulation main article: controlled ovarian hyperstimulation ovarian hyperstimulation is the stimulation to induce development of multiple follicles of the ovaries. it should start with response prediction by e.g. age, antral follicle count and level of anti-müllerian hormone. the resulting prediction of e.g. poor or hyper-response to ovarian hyperstimulation determines the protocol and dosage for ovarian hyperstimulation. ovarian hyperstimulation also includes suppression of spontaneous ovulation, for which two main methods are available: using a (usually longer) gnrh agonist protocol or a (usually shorter) gnrh antagonist protocol. in a standard long gnrh agonist protocol the day when hyperstimulation treatment is started and the expected day of later oocyte retrieval can be chosen to conform to personal choice, while in a gnrh antagonist protocol it must be adapted to the spontaneous onset of the previous menstruation. on the other hand, the gnrh antagonist protocol has a lower risk of ovarian hyperstimulation syndrome (ohss), which is a life-threatening complication. for the ovarian hyperstimulation in itself, injectable gonadotropins (usually fsh analogues) are generally used under close monitoring. such monitoring frequently checks the estradiol level and, by means of gynecologic ultrasonography, follicular growth. typically approximately 10 days of injections will be necessary. natural ivf main article: natural cycle in vitro fertilisation there are several methods termed natural cycle ivf: ivf using no drugs for ovarian hyperstimulation, while drugs for ovulation suppression may still be used. ivf using ovarian hyperstimulation, including gonadotropins, but with a gnrh antagonist protocol so that the cycle initiates from natural mechanisms. frozen embryo transfer; ivf using ovarian hyperstimulation, followed by embryo cryopreservation, followed by embryo transfer in a later, natural, cycle. ivf using no drugs for ovarian hyperstimulation was the method for the conception of louise brown. this method can be successfully used when women want to avoid taking ovarian stimulating drugs with its associated side-effects. hfea has estimated the live birth rate to be approximately 1.3% per ivf cycle using no hyperstimulation drugs for women aged between 40 and 42. mild ivf is a method where a small dose of ovarian stimulating drugs are used for a short duration during a natural menstrual cycle aimed at producing 2–7 eggs and creating healthy embryos. this method appears to be an advance in the field to reduce complications and side-effects for women, and it is aimed at quality, and not quantity of eggs and embryos. one study comparing a mild treatment (mild ovarian stimulation with gnrh antagonist co-treatment combined with single embryo transfer) to a standard treatment (stimulation with a gnrh agonist long-protocol and transfer of two embryos) came to the result that the proportions of cumulative pregnancies that resulted in term live birth after 1 year were 43.4% with mild treatment and 44.7% with standard treatment. mild ivf can be cheaper than conventional ivf and with a significantly reduced risk of multiple gestation and ohss. final maturation induction further information: final maturation induction when the ovarian follicles have reached a certain degree of development, induction of final oocyte maturation is performed, generally by an injection of human chorionic gonadotropin (hcg). commonly, this is known as the "trigger shot." hcg acts as an analogue of luteinising hormone, and ovulation would occur between 38 and 40 hours after a single hcg injection, but the egg retrieval is performed at a time usually between 34 and 36 hours after hcg injection, that is, just prior to when the follicles would rupture. this avails for scheduling the egg retrieval procedure at a time where the eggs are fully mature. hcg injection confers a risk of ovarian hyperstimulation syndrome. using a gnrh agonist instead of hcg eliminates most of the risk of ovarian hyperstimulation syndrome, but with a reduced delivery rate if the embryos are transferred fresh. for this reason, many centers will freeze all oocytes or embryos following agonist trigger. egg retrieval further information: transvaginal oocyte retrieval the eggs are retrieved from the patient using a transvaginal technique called transvaginal oocyte retrieval, involving an ultrasound-guided needle piercing the vaginal wall to reach the ovaries. through this needle follicles can be aspirated, and the follicular fluid is passed to an embryologist to identify ova. it is common to remove between ten and thirty eggs. the retrieval procedure usually takes between 20 and 40 minutes, depending on the number of mature follicles, and is usually done under conscious sedation or general anaesthesia. egg and sperm preparation in the laboratory, for icsi treatments, the identified eggs are stripped of surrounding cells (also known as cumulus cells) and prepared for fertilisation. an oocyte selection may be performed prior to fertilisation to select eggs that can be fertilised, as it is required they are in metaphase ii. there are cases in which if oocytes are in the metaphase i stage, they can be kept being cultured so as to undergo a posterior sperm injection. in the meantime, semen is prepared for fertilisation by removing inactive cells and seminal fluid in a process called sperm washing. if semen is being provided by a sperm donor, it will usually have been prepared for treatment before being frozen and quarantined, and it will be thawed ready for use. co-incubation demonstration of icsi the sperm and the egg are incubated together at a ratio of about 75,000:1 in a culture media in order for the actual fertilisation to take place. a review in 2013 came to the result that a duration of this co-incubation of about 1 to 4 hours results in significantly higher pregnancy rates than 16 to 24 hours. in most cases, the egg will be fertilised during co-incubation and will show two pronuclei. in certain situations, such as low sperm count or motility, a single sperm may be injected directly into the egg using intracytoplasmic sperm injection (icsi). the fertilised egg is passed to a special growth medium and left for about 48 hours until the egg consists of six to eight cells. in gamete intrafallopian transfer, eggs are removed from the woman and placed in one of the fallopian tubes, along with the man's sperm. this allows fertilisation to take place inside the woman's body. therefore, this variation is actually an in vivo fertilisation, not in vitro. embryo culture main article: embryo culture the main durations of embryo culture are until cleavage stage (day two to four after co-incubation) or the blastocyst stage (day five or six after co-incubation). embryo culture until the blastocyst stage confers a significant increase in live birth rate per embryo transfer, but also confers a decreased number of embryos available for transfer and embryo cryopreservation, so the cumulative clinical pregnancy rates are increased with cleavage stage transfer. transfer day two instead of day three after fertilisation has no differences in live birth rate. there are significantly higher odds of preterm birth (odds ratio 1.3) and congenital anomalies (odds ratio 1.3) among births having from embryos cultured until the blastocyst stage compared with cleavage stage. embryo selection further information: embryo quality laboratories have developed grading methods to judge ovocyte and embryo quality. in order to optimise pregnancy rates, there is significant evidence that a morphological scoring system is the best strategy for the selection of embryos. since 2009 where the first time-lapse microscopy system for ivf was approved for clinical use, morphokinetic scoring systems has shown to improve to pregnancy rates further. however, when all different types of time-lapse embryo imaging devices, with or without morphokinetic scoring systems, are compared against conventional embryo assessment for ivf, there is insufficient evidence of a difference in live-birth, pregnancy, stillbirth or miscarriage to choose between them. active efforts to develop a more accurate embryo selection analysis based on artificial intelligence and deep learning are underway. embryo ranking intelligent classification assistant (erica), is a clear example. this deep learning software substitutes manual classifications with a ranking system based on an individual embryo's predicted genetic status in a non-invasive fashion. studies on this area are still pending and current feasibility studies support its potential. embryo transfer main article: embryo transfer the number to be transferred depends on the number available, the age of the patient and other health and diagnostic factors. in countries such as canada, the uk, australia and new zealand, a maximum of two embryos are transferred except in unusual circumstances. in the uk and according to hfea regulations, a woman over 40 may have up to three embryos transferred, whereas in the us, there is no legal limit on the number of embryos which may be transferred, although medical associations have provided practice guidelines. most clinics and country regulatory bodies seek to minimise the risk of multiple pregnancy, as it is not uncommon for multiple embryos to implant if multiple embryos are transferred. embryos are transferred to the patient's uterus through a thin, plastic catheter, which goes through her vagina and cervix. several embryos may be passed into the uterus to improve chances of implantation and pregnancy. luteal support main article: luteal support luteal support is the administration of medication, generally progesterone, progestins,