You may have come across the terms "in vivo" and "in vitro" while reading medical studies or heard them used in regards to procedures like in vitro fertilization. But what do these terms mean, and what are their similarities and differences? Definition of In Vivo, In Vitro, and In Situ In vivo In Latin, in vivo means "within the living." The term refers to medical studies, clinical trials, or procedures done in a living organism, such as a laboratory animal or human. In vitro The term is Latin for "within the glass." It refers to a medical study, experiment, or procedure performed in a test tube, laboratory dish, or another controlled environment outside a living organism. In situ This means "in its original place," i.e., happening where it naturally occurs. For instance, carcinoma in situ, which refers to cancer in which abnormal cells have not spread to surrounding tissue or other areas of the body. Differences and Similarities Although in vivo and in vitro are different techniques, they are both done for the advancement of scientific research and human medicine to develop new treatments and better understand normal bodily functions. Below is the difference between in vivo and in vitro: In vivo testing is more expensive and takes longer to get results compared to in vitro testing.Most biological experiments are carried out using in vitro techniques despite in vivo testing producing more specific and detailed results as it looks at the actual effect on an organism, whether a laboratory animal or a human.In vivo testing has to adhere to more regulations because it uses live subjects. Real-Life Examples Here are some examples of how these methods are used in real life: 1. Medical studies and clinical trials Medical studies, such as monitoring the effects of a new drug, are usually done in vitro first to avoid subjecting humans or animals to the possible side effects or toxicity of the drug. If researchers wanted to look at the ability of a drug to treat cancer, they would grow cancer cells in a Petri dish, add the drug, and observe its effects on the cells. In vitro studies allow more rapid development of new treatment since many drugs can be studied simultaneously and allows for more detailed and accurate analyses owing to large sample sizes. Nonetheless, isolated cells grown in culture do not necessarily react the same way that cells inside a living organism would. If, for example, the chemotherapy drug is determined to be efficacious, then it can advance to in vivo tests. Usually, in vivo studies are first done in animals such as laboratory rats, which allows researchers to see how a drug acts amid other bodily processes. However, a drug that is effective in animals may not be effective in humans due to inherent differences in the species. Therefore, after animal testing, new medications undergo further in vivo testing during clinical trials to determine their effects on humans before being approved for general use. 2. Fertilization In vitro fertilization is used to treat infertility and is the most effective type of assisted reproductive technology (ART). It involves extracting mature eggs from the ovaries of the woman or egg donor, retrieving sperm from the woman's partner or a sperm donor, manually combining the egg and sperm in a laboratory dish. The fertilized egg (embryo) or eggs (embryos) then get transferred to the uterus of the woman or a gestational carrier. Related: Causes of Female infertility and its treatment IVF can be used to treat infertility if you or your partner has: Blocked or damaged fallopian tubesOvulation disorders such as infrequent or absent ovulationUterine fibroids, which can interfere with implantation of the fertilized eggProblems with sperm production, function, or deliveryPrevious tubal ligation or removalEndometriosisUnexplained fertilityA genetic disorderPreserved fertility through frozen embryos, eggs, or ovarian tissue Note: Women who don't have a functional uterus or cannot carry a pregnancy to term may choose IVF using a gestational carrier. One cycle of IVF can take about 2 to 3 weeks, and you may require more than one round. According to the Mayo Clinic, risks may include:- Multiple pregnanciesMiscarriageEctopic pregnancyPremature deliveryLow birth weightStressBirth defectsCancer Your chance of giving birth to a healthy baby through IVF will depend on various factors, including: Age: In the US, the live birth rate for each IVF cycle started is approximately 41-43% for women under age 35 and about 13-18% for women ages over 40, according to the American Pregnancy Association.Reproductive history: Women that have previously given birth are more likely to get pregnant using IVF than those who've never given birth.Embryo status: Transfer of more developed embryos is associated with higher pregnancy rates compared with less developed embryos (day two or three).Lifestyle factors: Smoking can lower a woman's chance of success using IVF by 50% while being obese can decrease your chances of getting pregnant and having a baby. 3. Antibiotic sensitivity Antibiotics are medicines used to treat or prevent bacterial infections. They work by killing bacteria or inhibiting their growth. As there are many types of antibiotics and each antibiotic is effective only against certain bacteria, if you have an infection, your doctor will prescribe the antibiotic that best combats the bacteria causing it. Where an infection may be as a result of many different types of bacteria or bacteria that are not predictably susceptible to antibiotics, a laboratory is asked to identify the infecting bacteria. Once identified, in vitro testing is done to check for the bacteria's susceptibility to a variety of antibiotics. The test results allow doctors to definitively determine which antibiotic they should use to treat the infection. However, antibiotics that are effective in the laboratory do not necessarily work in an infected person. The effectiveness of the treatment depends on: How well the drug is absorbed into the bloodstream (for drugs taken orally)How much of the drug reaches the sites of infection in the bodyHow quickly the body eliminates the drug In Vitro vs. In Vivo: The Takeaway Biomedical researchers use both in vivo and in vitro techniques to develop new drugs, diagnose conditions, and create new treatments. These techniques include cell cultures, clinical trials, animal testing, and biopsies. While each has its own advantages and disadvantages, in vitro testing is often combined with in vivo testing. The combination of approaches allows for more accurate results in regards to the overall effects of an experiment on a living subject.