How Sperm Freezing Works: The Process Step by Step

Sperm cryopreservation follows a short, well-defined clinical pathway: a consultation and written consent, infectious disease blood tests, two or three semen samples, a laboratory freeze and long-term storage in liquid nitrogen.

Key takeaways

• The usual steps are consultation and written consent, blood tests for HIV and hepatitis B and C, a semen sample after 2 to 7 days of abstinence, semen analysis, cryoprotectant, division into straws, slow cooling, and storage in liquid nitrogen at −196 °C.
• Cancer Research UK says most clinics recommend at least 2 samples, and 3 if possible, at least 2 days apart, so the collection phase can fit inside one week. For urgent cases, Saint Mary’s Hospital in Manchester says appointments are often the next working day.
• NHS Scotland says collection and processing usually take less than an hour per visit. The first visit is longer because of the consultation and consent paperwork.
• Conventional (slow) freezing is still the most widely used clinical method. A 2019 meta-analysis of 13 randomized trials found vitrification gave 6.98 percentage points higher post-thaw total motility, but it did not analyze pregnancies, and a 2019 review called a survival benefit not sufficiently demonstrated.
• Not all sperm survive thawing. In a 2015 split-sample study of 33 samples, progressive motility fell from about 56% fresh to about 31% after slow freezing.
• Thawed sperm are used in IUI, IVF or ICSI in the same way as fresh sperm. The HFEA states that IVF using frozen sperm is just as successful as IVF using fresh sperm.

Step 1: The consultation and consent

The process begins with a consultation with a reproductive scientist or another member of the andrology team. At the Hewitt Fertility Centre in Liverpool this covers the implications of storing sperm, the consent forms and your questions; Saint Mary’s Hospital in Manchester sends a text-message link to its online consent platform beforehand so you can register, upload photo ID and complete some forms in advance.

Under UK law you must state in writing how long you want your sperm stored, whether a named partner may use it, what should happen if you die or lose capacity, and whether unused samples may go to research or training. The HFEA adds that you can vary or withdraw consent at any time before the sperm are used. In the United States the paperwork is a storage agreement with the sperm bank; our guide on questions to ask your clinic lists the contract points worth checking, including what happens if storage fees go unpaid.

Step 2: Infectious disease screening

Before or at the first visit, a blood sample is screened for HIV, hepatitis B and hepatitis C. Gloucestershire Hospitals NHS Foundation Trust states that the HFEA “requires testing of blood for HIV, Hepatitis B and C before storage” and adds a screen for sexually transmitted infections, with extra tests possible depending on travel history. Gloucestershire takes blood and urine two weeks before the first appointment so the results are back before storage; the Hewitt Fertility Centre takes blood at the appointment itself.

A positive result does not stop you freezing. The HFEA says testing has no bearing on whether you can freeze your sperm; affected samples are stored separately to prevent contamination of other samples. Gloucestershire notes that, depending on the result, storage may have to take place at a larger storage center.

In the United States, sperm banks are regulated by the FDA under 21 CFR Part 1271. Its donor-eligibility rules are written for donor sperm: section 1271.90 says a donor-eligibility determination and donor screening and testing are not required for “cells and tissues for autologous use” or for “reproductive cells or tissue donated by a sexually intimate partner of the recipient for reproductive use”. A specimen stored for autologous use must be labeled “FOR AUTOLOGOUS USE ONLY”, and one without all otherwise applicable screening and testing must be labeled “NOT EVALUATED FOR INFECTIOUS SUBSTANCES”. Ask your sperm bank whether it tests at intake and which results a fertility clinic will need before it uses a sample.

Step 3: Preparing for and producing the sample

Clinics ask for a period of abstinence before each sample; Cancer Research UK says this helps collect the highest number of sperm. The WHO laboratory manual (6th edition, 2021) specifies a minimum of 2 and a maximum of 7 days for semen analysis; Saint Mary’s puts it as “at least 48 hours but no longer than 7 days”, and Cancer Research UK suggests 3 or 4 days. Saint Mary’s recommends attending even if you have not managed this.

The sample is produced by masturbation into a sterile container in a private room at the clinic. Saint Mary’s explains that freezing takes place as soon as possible after the sample is produced, which is why it prefers samples produced in its department. If you cannot produce on site, some units accept a sample produced at home: the Hewitt Fertility Centre does in some circumstances if it reaches the laboratory within one hour, and Cancer Research UK says you usually need a special condom or pot provided by the clinic. Gloucestershire allows off-site production only in exceptional circumstances, so ask in advance.

Step 4: Semen analysis

Every sample is analyzed before it is frozen: volume, sperm concentration, total sperm number, motility (how many sperm are moving, and how well) and morphology (the proportion with a normal shape). Results are compared with the lower reference limits in the WHO laboratory manual for the examination and processing of human semen, 6th edition (2021). These limits are the 5th centile of men whose partners conceived naturally within a year, so a result below a limit does not mean infertility, and one above it does not guarantee fertility.

Source: Manchester University NHS Foundation Trust reprint of the WHO 6th edition table (Campbell et al.).

Samples below these limits are still frozen. Gloucestershire’s leaflet is clear: “Provided there are at least a few sperm present, each sample will be frozen and stored.” A low count or low motility may mean the clinic asks for more samples, and makes ICSI, which needs only one sperm per egg, the more likely treatment later; see how many samples to freeze. Saint Mary’s telephones the result through on the same day.

Step 5: Cryoprotectant, straws and freezing

Ice crystals forming inside a sperm cell cause mechanical damage, so the laboratory first mixes the semen with a cryoprotectant, a medium that usually contains glycerol and egg yolk. The 2019 EMJ Reproductive Health review notes that “the addition of glycerol has to be done progressively”, because glycerol enters the cell more slowly than water and changes in cell volume must be controlled.

The mixture is divided into small containers (straws, vials or ampoules, depending on the clinic) so that not all of it has to be thawed at once. Each is labeled and coded for identification; at Saint Mary’s the label carries your name, date of birth and reference number, and a second member of staff witnesses and checks it.

Slow freezing versus vitrification

In the protocol described by the EMJ review, conventional slow freezing cools the sample at 1 to 10 °C per minute to about −80 °C, holds it in liquid nitrogen vapor for 20 minutes and then plunges it into liquid nitrogen; the whole procedure takes 30 minutes to an hour. Vitrification uses ultra-rapid cooling so the medium solidifies into a glass-like state without ice crystals.

The meta-analysis authors also noted that their results are limited by the small number of studies and the variety of vitrification protocols. The EMJ review is more cautious: “conventional freezing is still the most widely used protocol for clinical purposes”, and it is “not sufficiently demonstrated that sperm vitrification improves survival significantly” more than freezing methods. A 2015 split-sample study of 33 samples (Mohamed) found no significant difference between the two methods in progressive motility, viability or mitochondrial membrane potential. The review also lists cross-contamination from direct contact with liquid nitrogen as a drawback of non-aseptic vitrification.

Step 6: Storage at −196 °C

Frozen straws go into containers called dewars, kept at about −196 °C. The Hewitt Fertility Centre keeps straws “in liquid nitrogen or liquid nitrogen vapour”; Saint Mary’s stores ampoules in liquid nitrogen vapor at approximately −196 °C.

Tanks are monitored and, at Gloucestershire, linked to the hospital switchboard; that unit also splits each patient’s ampoules across two tanks. Gloucestershire and the Hewitt Fertility Centre both say they cannot accept responsibility for loss due to equipment failure, and Saint Mary’s also mentions interruptions to the liquid nitrogen supply, so look for this clause in any storage agreement.

How long samples may stay is set by law and contract. The HFEA says there is not enough evidence to say for sure whether longer storage has any negative impact on viability; Guinness World Records lists a successful IVF treatment in New York in 2015 using sperm stored for 27 years and 195 days. In the UK the statutory maximum is 55 years with consent renewed every 10 years; other countries differ, see sperm storage limits by country. Clinics may dispose of samples if fees go unpaid or you cannot be contacted, so keep your contact details current.

Step 7: Thawing, the post-thaw check and later use

When needed, a straw is warmed, usually in a water bath, then washed and centrifuged to remove the cryoprotectant, and the laboratory counts how many sperm are moving. Saint Mary’s describes thawing one ampoule at a clinician’s request to assess “the suitability of your sample for use in fertility treatment”, and it has a separate test-thaw consent form.

Some loss is normal. In the 2015 split-sample study, which froze washed or swim-up-prepared sperm, progressive motility fell from about 56% fresh to about 31% after slow freezing and 34% after vitrification, and the share of live sperm fell by 45 to 51% with either method. The Hewitt leaflet states that “there is always a small reduction in sperm quality due to the freeze-thaw process”; see does freezing damage sperm.

The thawed sperm are then used in one of three treatments:

• IUI (intrauterine insemination): prepared sperm are placed directly into the uterus around ovulation. This needs the largest number of motile sperm.
• IVF (in vitro fertilization): eggs and sperm are combined in a dish in the laboratory.
• ICSI (intracytoplasmic sperm injection): a single sperm is injected into each egg, so very few motile sperm are needed; the HFEA describes it as the option when sperm quality is not optimal.

The HFEA states that “IVF using frozen sperm is just as successful as IVF using fresh sperm”. IUI is more nuanced. In a 2023 single-center study of 5,335 IUI cycles from 2004 to 2021 at Massachusetts General Hospital (Cherouveim et al., Frontiers in Reproductive Health), motility was nearly identical (52.7% vs 52.6%) but frozen samples held far fewer motile sperm (mean total motile count 14.3 vs 65.0 million). The unadjusted clinical pregnancy rate per cycle was 9.4% with frozen vs 13.0% with fresh sperm, a difference that was not statistically significant overall after adjustment, although time to conception was longer (3.84 vs 2.58 cycles). Of the frozen-sperm cycles, 96.3% used anonymous donor sperm, so the figures do not directly describe men using their own banked samples; see frozen vs fresh sperm success rates. Outcomes depend on both partners, so ask a fertility specialist what is realistic for you.

What to expect at the appointment

The sequence below is drawn from NHS patient leaflets; private clinics and US sperm banks follow a similar order, though the paperwork differs.

How long does it take?

• Per visit: NHS Scotland says collection and processing are “usually taking less than an hour”. Allow longer for the first visit, which includes the consultation, consent forms and often a blood draw.
• Whole process: at least 2 samples, and 3 if possible, at least 2 days apart (Cancer Research UK), so it can be complete within about one week.
• Urgent cases: Saint Mary’s says appointments are usually made quickly, “often the next working day”.
• Results: same-day telephone call at Saint Mary’s; NHS Scotland says the laboratory team contacts you about the sample’s quality and whether it is suitable for freezing.

Bring photo ID and, if you want a partner named on your consent, their full name, date of birth and health service number. Fees vary widely; the cost calculator estimates the total for your samples and storage years, and the sperm bank directory lists laboratories by country.

This guide describes a standard pathway, not individual medical advice. Ask your urologist, oncologist or fertility specialist how quickly you should bank and how many samples they recommend.