Fertility

Preliminary or Final: Which SART Data Year You're Reading

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The most recent fertility statistics you can find are almost never finished. Because a live birth cannot be counted until a pregnancy delivers, the freshest reporting year is still filling in, and its numbers shift as outcomes mature. Knowing the difference between a preliminary and a final data year keeps you from comparing a half-counted clinic to a fully-counted one.

Last updated: July 2026

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What 'preliminary' and 'final' mean

Fertility data is labeled by the year a cycle started, and each year passes through a preliminary stage before it is final. A year is preliminary when its cycles have begun but not every pregnancy has been followed through to a recorded outcome; it becomes final once all of those births — and losses — are counted. Live-birth delivery is the success measure that takes longest to settle, because it cannot be recorded until the baby is actually born 1.

The practical effect is that the newest year on a clinic's or a registry's page is a moving target. Pregnancy-based figures are available early, but the live-birth numbers most people actually care about keep maturing for months after the cycles themselves are finished.

Why live-birth data lags by roughly two years

Live-birth data trails the cycle year by about two years, and the reason is plain arithmetic. A cycle leads to an embryo transfer, a transfer that works becomes a pregnancy, and a pregnancy runs about nine months before a birth can be counted — then the outcome has to be reported and compiled. A live birth cannot appear in the statistics until it has happened 1.

So the most recent year with complete live-birth outcomes is always a couple of years behind the calendar. That is not a flaw in the data; it is what honest live-birth counting requires. A registry that published final birth rates for cycles started only months ago would be guessing, not reporting.

Which year the CDC and SART are showing now

The reporting year on the page tells you how settled the numbers are. The CDC's most recent national summary reflects cycles started in 2022 and is published as an online dashboard 2, while earlier years such as 2021 were released as full written reports 3. Federal law has required this reporting since 1992, and the CDC's success-rate pages are the official home for it 4.

SART likewise lets you select a data year in its online reports, and older years carry final outcomes while the newest may still be preliminary 5. When two sources seem to disagree, the first thing to check is whether they are simply showing different sart data years.

Why a preliminary year can mislead

A preliminary year tends to look different from a final one, usually in a predictable direction. Early figures often lean on pregnancies rather than confirmed live births, and not every pregnancy becomes a live birth, so a preliminary live-birth rate can shift downward as losses are counted 1. Comparing one clinic's preliminary year against another clinic's final year is comparing a half-counted number to a finished one.

A preliminary year and a final year are not the same measurement, so they should not be placed side by side. SART reports success across several groupings — per retrieval, per transfer, per patient — and mixing a preliminary figure in one grouping with a final figure in another only compounds the error 5.

How to read the year and status correctly

Reading fertility data safely comes down to three checks: which year, preliminary or final, and which denominator. Match all three before comparing clinics or judging a trend. If you are working out how to read SART success rates, the data year and its status are the first things to confirm, because a difference that looks like clinic quality can turn out to be a difference of one reporting cycle 5.

When a number is preliminary, treat it as provisional — useful for a rough sense, not for a fine ranking. When it is final, it will not move. Keeping the preliminary-or-final distinction in view is basic data hygiene for anyone comparing programs.

Using a personal estimate instead of one shaky year

When the newest year is still preliminary, an individualized estimate is often steadier ground than a single clinic's provisional number. The CDC's IVF Success Estimator draws on compiled national data to project a personal live-birth estimate from age, height and weight, and diagnosis, for ages 20 to 50 6. Because it rests on settled national figures rather than one clinic's newest, half-counted year, it gives a more stable baseline.

That baseline does not replace a clinic's own report, but it anchors it. A clinic's preliminary year then becomes one data point beside a national estimate, rather than the whole basis for a decision.

Common questions

Because they do not exist yet in final form. A cycle started this year cannot produce a countable live birth until a pregnancy runs its course and the outcome is reported, which takes roughly two years to complete. The freshest data available is preliminary — cycles and pregnancies are recorded, but the live-birth totals are still filling in.

Not wrong, just unfinished. Preliminary figures are accurate for what has been counted so far, but the live-birth rate can still move as remaining pregnancies deliver and any losses are recorded. Treat a preliminary year as provisional: fine for a rough sense of a clinic, not solid enough for ranking one program against another.

Usually about two years. A cycle has to lead to a transfer, a pregnancy, and roughly nine months of gestation before a birth can be counted, and then the results are compiled. That is why the most recent fully final national data typically reflects cycles started two calendar years earlier, not the current year.

Preliminary figures often rest on pregnancy rates, and not every pregnancy becomes a live birth. As losses are counted and the year finalizes, a live-birth rate can settle lower than the early number suggested. A newer year that appears better may simply be earlier in that maturing process, not evidence of improvement.

Roughly, but not identically. Both are keyed to the cycle-start year and both lag for the same live-birth-counting reason, yet their publication schedules and formats differ — the CDC now uses an online dashboard, while some years appeared as written reports. If the two seem to disagree, check whether you are looking at the same data year first.

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Comparing fertility data years without being fooled

  • —A clinic quoting its newest, preliminary success rate against another clinic's older, final number as if the two were equivalent.
  • —A success figure with no data year attached at all, so you cannot tell whether it is preliminary or final.
  • —A pregnancy rate presented as a live-birth rate, or a preliminary pregnancy figure used to imply a settled birth outcome.

This article explains how fertility data years are reported and why they lag; it is educational and not medical advice. How any figure applies to your own odds is a discussion for a fertility clinician who knows your history.

References

  1. 1.Centers for Disease Control and Prevention (2024). NASS Technical Notes. CDC National ART Surveillance System. linkART success measures are defined so that a live-birth delivery is counted only after the birth occurs, and national figures are noncumulative single-year measures — the methodological basis for why the newest year is provisional until outcomes mature.
  2. 2.Centers for Disease Control and Prevention (2024). National ART Summary (2022 data dashboard). CDC Division of Reproductive Health. linkThe most recent federal national summary reflects cycles started in 2022 and is published as an online dashboard, illustrating how the current data year is labeled.
  3. 3.Centers for Disease Control and Prevention (2023). 2021 Assisted Reproductive Technology: Fertility Clinic and National Summary Report. CDC / US Department of Health and Human Services. linkEarlier ART data years, such as cycles started in 2021, were released as full written national summary reports, showing the finalized prior-year format.
  4. 4.Centers for Disease Control and Prevention (2024). ART Success Rates. CDC Division of Reproductive Health. linkFederal law has mandated ART success-rate reporting since 1992, and the CDC's success-rate pages are the official source where each data year is published.
  5. 5.Society for Assisted Reproductive Technology (SART) (2024). National Summary Report (SART CORS Online). Society for Assisted Reproductive Technology. link ✓SART's online reports are selectable by data year and report success across several groupings (per retrieval, per transfer, per patient), so the year and its preliminary-or-final status must be matched before comparing figures.
  6. 6.Centers for Disease Control and Prevention (2024). IVF Success Estimator. CDC Division of Reproductive Health. linkThe CDC IVF Success Estimator produces an individualized live-birth estimate from compiled national data by age, height and weight, and diagnosis for ages 20 to 50 — a stable baseline that does not hinge on one preliminary clinic year.

6 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — citations link their sources. Editorial policy

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