The severity or complexity of infertility for you and your partner as a whole is also critical. Generally, patients are characterized as “subfertile” if there is only one infertility factor such as mild endometriosis, which can be improved through surgeries like laparoscopy. However, if both partners contribute infertility factors or one partner has multiple infertility factors, the chance of IVF success is significantly decreased.
A review in 2013 came to the result that infants resulting from IVF (with or without ICSI) have a relative risk of birth defects of 1.32 (95% confidence interval 1.24–1.42) compared to naturally conceived infants.[48] In 2008, an analysis of the data of the National Birth Defects Study in the US found that certain birth defects were significantly more common in infants conceived through IVF, notably septal heart defects, cleft lip with or without cleft palate, esophageal atresia, and anorectal atresia; the mechanism of causality is unclear.[49] However, in a population-wide cohort study of 308,974 births (with 6,163 using assisted reproductive technology and following children from birth to age five) researchers found: "The increased risk of birth defects associated with IVF was no longer significant after adjustment for parental factors." [50] Parental factors included known independent risks for birth defects such as maternal age, smoking status, etc. Multivariate correction did not remove the significance of the association of birth defects and ICSI (corrected odds ratio 1.57), although the authors speculate that underlying male infertility factors (which would be associated with the use of ICSI) may contribute to this observation and were not able to correct for these confounders. The authors also found that a history of infertility elevated risk itself in the absence of any treatment (odds ratio 1.29), consistent with a Danish national registry study [51] and "implicates patient factors in this increased risk." The authors of the Danish national registry study speculate: "our results suggest that the reported increased prevalence of congenital malformations seen in singletons born after assisted reproductive technology is partly due to the underlying infertility or its determinants."
The best study in the field enrolled 750 women to receive clomid or letrozole, followed them for 5 courses of therapy and revealed that the group receiving letrozole had higher live birth rates and fewer multiple gestations. The data is of exceptional quality, and there’s no reason to believe the conclusion doesn’t also apply to the choice of drugs if these patients proceeded on to IUI.
Complexity. IUI refers to one procedure. Prepared sperm is placed directly in the patient’s uterus when she is ovulating in order to aid fertilization. IUI may be performed in sync with a woman’s natural cycle or timed with fertility medications to stimulate ovulation. IVF, on the other hand, is a process which consists of several stages and requires more than one procedure: first the ovaries are stimulated using a series of fertility medications, then the patient undergoes egg retrieval in a day procedure under a mild anesthetic, then after embryos have been created and incubated in the lab, they are placed directly into her uterus in the embryo transfer procedure. Even with the use of fertility drugs, going through IUI is less physically demanding than undergoing IVF.

While ICSI is a more invasive procedure, some have suggested it may help by reducing the risk of failed fertilisation. However, it's emerging that IVF is probably the preferred treatment, at least in the first cycle, in "unexplained" infertility. IVF allows for healthy competition between sperm, is less expensive, avoids trauma to the egg and may produce more embryos, with better pregnancy and live birth rates  
Assisted hatching. About five to six days after fertilization, an embryo "hatches" from its surrounding membrane (zona pellucida), allowing it to implant into the lining of the uterus. If you're an older woman, or if you have had multiple failed IVF attempts, your doctor might recommend assisted hatching — a technique in which a hole is made in the zona pellucida just before transfer to help the embryo hatch and implant. Assisted hatching is also useful for eggs or embryos that have been previously frozen as the process can harden the zona pellucida.
Repeated failed rounds of IVF can help identify causes of infertility. For example, if sperm and egg quality are normal, then the conception issue may be rooted at the embryonic or implantation level. In other words, if IVF fails to result in pregnancy despite successful fertilization, embryonic development or implantation may be to blame. Still this is a very expensive way to start getting answers.